Thinking about an ex while you're with someone else

The letter ran in Dear Abby on October 28. The writer is 39 and has been with her husband for 20 years. Several exes have reached out over the last 18 months, and one of them takes up more of her thoughts than she wants. Nothing has happened in person. She feels she missed out on dating around when she was younger, and she says she can’t talk to anyone else about it.1

If some version of that sounds familiar, the thoughts on their own aren’t a verdict on you as a partner. It does raise a question worth answering honestly: what are the thoughts actually about?

Three things that tend to feed it

Fear of being alone. A 2016 study looked at people right after breakups, using daily check-ins for a month. On days when people felt a stronger fear of being single, they reported more longing for their ex and made more attempts to get back together.2 That research was about people who had just split up, not people in a new relationship. But the mechanism, longing that rises with worry about your own future, is worth checking for. Sometimes the ex is a stand-in for security.

How things are at home. A 2024 study followed 542 adults aged 22 to 35 who were in relationships and had a crush on someone else. Stronger attraction went with lower quality in the main relationship. Few people actually got involved with the crush over four months, but lower relationship quality was linked to breakups later.3 The sample was younger than you, and it can’t say which came first. Still, it points at the main relationship rather than the other person.

Contact, even passive. Vice reported in October 2026 on Tara Marshall’s research, nearly 800 participants across four studies: seeing an ex on social media raised sadness, jealousy and breakup distress, and stumbling onto their photos by accident could be just as upsetting as looking on purpose.4 Those studies were about getting over a breakup, but the point may carry over: each glimpse seemed to stir things back up.

What the advice columns get right

Abby’s answer was blunt: don’t risk a solid relationship for a what-if, block him, and if you need to rekindle things, see a licensed couples counselor, together or alone.1 That fits the research better than it might seem. The contact piece is about turning down the input. The counselor piece is about the relationship you’re actually in.

A few practical steps that follow from the above:

• Close the channel. Mute, unfollow or block. You can decide later whether to undo it.
• Separate the person from the feeling. Is it them, or being young, or being wanted in a new way?
• Look at what’s happening with your partner. Not as a confession, but as a question to yourself about what’s been missing.

If the ex is someone you’re still actively in touch with, still close with an ex covers that situation directly. And if the thoughts are less about the ex and more about whether you chose right, am I settling in my 40s may be the more useful read.

What this doesn’t tell you

• None of these studies looked at people in long marriages thinking about an ex from decades ago.
• The findings are correlational. They describe patterns, not what’s going on in your head.
• A letter to an advice column is one person’s story, not data. It’s here because it describes the feeling clearly.