Should you worry when he mentions other girls he's dated?

Look at what he's doing with the mention, not just that he made it. A casual line about a date from last week, followed by a question about your day, is a guy making conversation. A story that spends most of its length on what was wrong with her, or a comparison that lands on you, is a different thing. Notice whether the other women appear as people or as punchlines. Notice whether he's asking how you feel about it, which can be a fishing move, or whether he's just telling you something. A single mention rarely means much. A pattern where every story is about another woman and you're always the one being measured against her is worth taking seriously.

Also notice timing. If he mentions another date within days of you two starting to see each other, that's common and mostly means he's still active. If he keeps bringing up one particular ex or recent date after you've said you're not interested in hearing about it, that's a clearer sign he isn't respecting the boundary.

A good reply takes the mention at face value without giving it more weight than it has. Acknowledge what he said in a line, so he knows you heard it. Then return the conversation to something about you or the two of you. The move is to show that his dating history is background, not the main topic. If he tries to pull you into a detailed discussion of the other woman, you can decline with a light answer and change the subject. You're not refusing to talk about it. You're just not making it the centre of the exchange.

It also helps to keep your own interest visible. When he's talking about someone else, a little warmth directed at him, or a question about something he's into, reminds him you're the one he's talking to now. Avoid matching his story with one of your own unless it's clearly a shared, relaxed exchange. Matching tends to turn a light mention into a competition.

Don't decide what the mention means in the moment. Give it a few days and watch what he does next. If he keeps making plans, reaches out without prompting, and is interested in your life, the mention was probably just the normal chatter of someone who dates. If he goes quiet after you answered calmly, that's information too, though it could be about his own schedule or nerves rather than about you.

If he brings up the other women again and again, or if he starts treating you differently in ways that feel like a comparison, you can name it once in a calm, plain way. Something like saying you'd rather not hear about his other dates and asking what he'd like to talk about instead. If he responds with respect, that's a good sign. If he dismisses the request or keeps doing it, you have your answer, and you can stop investing time in him without needing to prove anything.