What Is Infidelity? A Couples Guide & Relationship Boundary Workbook
Author: Dr. Mary Perleoni, Ph.D., LMHC
Published September 9, 2025
Key Points: What You’ll Learn in This Guide
Infidelity isn’t just sex outside a relationship — it’s any betrayal of trust, including physical, emotional, or digital boundaries.
Emotional affairs can be just as painful as physical ones, often involving secrecy, late-night conversations, or turning to someone else for emotional intimacy.
Clear boundaries prevent betrayal — couples who openly define physical, emotional, digital, and social limits build stronger, more secure relationships.
The Relationship Boundary Workbook helps couples talk through expectations, with guided prompts to define monogamy, honesty, privacy, and repair strategies.
Why Infidelity Is More Complex Than You Think
When most people hear the word infidelity, they picture a painful but seemingly straightforward scenario: “My partner had sex with someone else while we had an agreement to be monogamous.”
But in my work as a therapist specializing in couples recovering from betrayal, I’ve seen that infidelity is far more complex than just physical affairs. For many couples, the deepest hurt comes from broken boundaries they never explicitly discussed — late-night texts, emotional closeness with someone else, or secrecy around digital interactions.
The reality is infidelity happens whenever there’s a betrayal of trust and an unspoken or spoken boundary is crossed.
Defining Infidelity
Infidelity can be defined as breaking an agreed-upon expectation of exclusivity, secrecy, or loyalty within a committed relationship.
This breach may involve:
Physical intimacy (sex, kissing, touching, strip clubs, etc.)
Emotional closeness (sharing vulnerabilities, late-night conversations, or secret attachments)
Digital interactions (private messaging, deleting texts, or hiding online activity)
At its core, infidelity is not just about sex — it’s about betrayal of trust.
Emotional Infidelity: The Hidden Betrayal
Emotional infidelity is when a partner forms a secret or boundary-crossing emotional bond with someone outside the relationship—diverting intimacy, time, or romantic energy away from their partner. There may be no physical contact, but the priority shift, secrecy, and exclusivity create a breach of trust.
How it shows up (common patterns):
Ongoing private conversations (late-night texts/DMs) that you hide or minimize.
Sharing vulnerabilities, excitement, or day-to-day details with someone else before your partner.
Comparing your partner unfavorably to the other person or idealizing that relationship.
Deleting messages, using nicknames, or changing notification settings to avoid discovery.
Why it hurts so much:
Emotional affairs erode the secure bond at the heart of the relationship. Your partner experiences a loss of emotional safety and exclusivity—often compounded by secrecy—so the betrayal can feel as destabilizing as a physical affair.
Physical Infidelity: Beyond “Sleeping With Someone Else”
Physical betrayal feels more obvious — but even here, couples rarely agree 100%.
Is kissing someone at a party cheating?
Is dancing closely with someone inappropriate?
Is going to a strip club okay if there’s “no touching”?
What seems “harmless fun” to one partner may feel like deep betrayal to the other.
In open or non-monogamous relationships, the lines can be less defined. Multiple sexual partners may be acceptable, but only within specific agreements (for example, honesty about partners, safe-sex practices, or not mixing romance with physical intimacy). A betrayal happens when those agreements are broken — like hiding encounters, lying about partners, or disregarding shared rules.
Why Boundaries Are Everything
The couples who thrive after betrayal (and those who prevent it entirely) are the ones who define their boundaries clearly and revisit them often.
Without clear boundaries, people default to assumptions — which often don’t match. These conversations may feel uncomfortable at first, but they build security, intimacy, and trust.
That’s why I created the Relationship Boundary Workbook below. Use it as a tool to spark conversation and prevent misunderstandings.
The Relationship Boundary Workbook
Each section begins with a guiding philosophy, then offers questions you can answer together. Circle “Yes,” “No,” or “Needs Discussion.” Add your own. This is about defining your relationship — not living by anyone else’s rules.
This workbook is designed for couples at every stage of their relationship. It can be a powerful tool for those early in dating who want to start with clarity, for couples in committed relationships seeking to strengthen trust, and for those who have been married 20+ years but are facing new challenges in connection and intimacy. No matter where you are, the goal is the same: to create shared understanding and prevent painful misunderstandings.
The Relationship Boundary Workbook
Each section begins with a guiding philosophy, then offers questions you can answer together. Circle “Yes,” “No,” or “Needs Discussion.” Add your own. This is about defining your relationship — not living by anyone else’s rules.
Physical Boundaries
Physical connection can be innocent or intimate depending on context. What feels safe for one person may feel threatening for another. Defining this protects both partners.
Questions to explore:
Is holding hands with someone else okay?
Would a kiss (on the lips or cheek) count as betrayal?
How do we feel about close dancing at parties or weddings?
Are strip clubs or bachelor/bachelorette parties off-limits?
Is flirting with someone in public crossing a line?
If physical boundaries are crossed unintentionally (e.g., a hug from a friend), how should it be handled?
Does the identity of the other person matter (coworker, friend, stranger)?
How do alcohol or social settings impact what feels acceptable?
Emotional Boundaries
Emotional intimacy belongs at the heart of your relationship. Sharing deeply with someone else can feel like shifting loyalty away from your partner.
Questions to explore:
Is venting about our relationship to a coworker okay?
Should we disclose if an ex contacts us?
Is it acceptable to share secrets with a friend of another gender?
Are late-night texts with a colleague appropriate?
Is “harmless” flirting over text betrayal?
How much sharing with friends is healthy, and when does it feel like a threat?
Do we expect to be each other’s “first call” in times of need?
What level of privacy is acceptable in emotional conversations?
Digital Boundaries
Phones, apps, and social media are modern gateways for secrecy. Deciding together what transparency looks like prevents small issues from snowballing into big betrayals.
Questions to explore:
Is deleting messages okay, or is that a red flag?
Should we share passwords, or is privacy important?
Are private DMs with someone of the opposite sex acceptable?
How do we feel about following or liking “thirst traps” on Instagram?
Is consuming pornography okay? What are our limits?
How do we feel about reconnecting with old flames online?
Should we always disclose if someone flirts digitally?
How much digital privacy do we each expect?
Social Boundaries
Friendships are healthy, but without clarity, they can spark conflict. Discuss where companionship ends and betrayal begins.
Questions to explore:
Is one-on-one time with a friend of the opposite sex okay?
Are work dinners with colleagues acceptable?
What about traveling with a coworker of another gender?
Should we disclose if someone expresses attraction to us?
Are secret friendships acceptable?
How often do we prioritize partner vs. friends?
How do group settings vs. private hangouts affect comfort levels?
What role does alcohol or nightlife play in these dynamics?
Commitment Boundaries
Every couple has a unique agreement on loyalty. Clarifying what commitment means prevents assumptions and strengthens trust.
Questions to explore:
What does monogamy mean to each of us?
Is emotional connection outside the relationship ever acceptable?
How do we handle attraction to others — do we disclose it?
Do we agree to immediate honesty if a boundary is crossed?
How do we repair if something happens?
Should we revisit these boundaries regularly?
How do we talk about fantasies, desires, or needs safely?
Are there circumstances where flexibility is allowed (travel, long distance, etc.)?
Commonly Asked Questions About Cheating & Infidelity
What counts as cheating in a relationship?
Cheating is any behavior that breaks the trust or agreements in your relationship. For some couples, it’s limited to sexual contact with someone else. For others, it may include emotional secrecy, flirting, or online interactions. The core issue is whether a partner has crossed a boundary that violates the couple’s shared expectations of loyalty and honesty.
Is late-night texting with a coworker emotional infidelity?
It can be. Work-related communication is usually fine, but if texts become personal, secretive, or emotionally intimate — especially late at night — it may cross into emotional infidelity. A good rule of thumb: if you’d feel uncomfortable showing the messages to your partner, the boundary is probably being crossed.
How do we set boundaries that prevent betrayal?
Start by talking openly about what feels safe versus what feels like crossing a line. Agree on transparency around friendships, texting, social media, and travel. Boundaries aren’t about control — they’re about protecting trust and reducing gray areas where betrayal can occur. Revisit these agreements as your relationship evolves.
What’s the difference between physical and emotional affairs?
A physical affair involves sexual or romantic contact, such as kissing or sex, outside the relationship. An emotional affair happens when someone forms a secret, intimate emotional bond with another person, often sharing closeness and affection that should stay within the relationship. Both can be deeply painful because they divert intimacy away from the partnership.
