He said exclusive but keeps messaging other women

If he agreed to exclusive and still talks to other girls, he's testing whether the boundary is real and whether you'll enforce it. Or he's decided exclusivity means something different to him than to you, like no dating apps but texting is fine. Or he never believed the exclusivity conversation was binding.

Pay attention to his tone and speed. Is he hiding it from you, or is he casual about it? Hiding it means he knows it's wrong. Casual means he doesn't think it is. Both are problems, but they tell you something different about what he's actually willing to commit to. The messaging itself is the signal. His response to being called out is what tells you if this stops or if you're dealing with someone who won't respect your boundaries.

Your reply needs to do two things. First, name exactly what you saw or heard. Not interpretation, not suspicion, not how it makes you feel. The fact. Second, remind him what he agreed to. Keep it short and clear. Don't ask him why or give him room to reframe it as innocent.

Then stop. Let him respond. He will either own it and stop, make excuses, or get defensive. If he tries to argue that exclusivity doesn't cover texting other girls, that's your answer about whether he actually meant what he said. Don't keep explaining. You already explained that when you both agreed to be exclusive.

Send this during the day when you're calm, not late at night. Give him at least 24 hours to respond. If he doesn't text back within a day, that's a choice too. It means he's avoiding the conversation because he knows he's wrong.

If he apologizes and stops, you move forward. If he deflects or argues, you decide whether that's someone you keep dating. Do not repeat yourself or send multiple messages about it. One conversation. Clear boundary. His move. If he breaks it again after this, you don't need to have the conversation a third time. You just leave.