It’s better to look at this topic with nuance instead of assuming fixed “rules.” Attraction or emotional attachment outside a marriage can happen for many reasons (loneliness, unmet needs, excitement, emotional disconnect), and not every situation looks the same.
That said, when someone becomes strongly preoccupied with another person, there are some common behavioral patterns you might notice:
1. She thinks about him frequently
He’s often on her mind—she may seem distracted or mentally elsewhere.
2. She finds reasons to communicate
Texting, calling, or interacting more than necessary, even over small or trivial things.
3. She puts extra effort into her appearance (around him)
Dressing up more or paying special attention to how she looks when she expects to see him.
4. She compares him to her husband
Mentally or verbally, she may start noticing differences and idealizing the other person.
5. She becomes emotionally invested
She shares personal thoughts, problems, or feelings with him instead of her partner.
6. She hides interactions
Deleting messages, being secretive with her phone, or avoiding mentioning him.
7. Her mood depends on him
She feels unusually happy after contact—or upset when he’s distant.
8. She creates opportunities to see him
Finding excuses to be in the same place or extending conversations and meetings.
9. She feels conflicted or guilty
Even if she doesn’t act physically, there’s often an internal struggle between desire and commitment.
Important perspective
These signs don’t automatically mean “obsession” or wrongdoing. Sometimes they point to emotional needs not being met in the marriage, rather than just attraction itself.
If you’re asking because of a real situation, I can help you analyze it more specifically or figure out what to do next.