Great question Megan! Most guys will say, "It's no big deal, we're just friends." And it's true. What your question tells us is that your intuition, your gut feeling, is triggered. You have mentioned that there are some things in your past that may be contributing to your unease. It is important to clean those up so you can see your partner for who they are, not through the lense of the guys in your past. And this will help you have a better conversation with your guy.
First, find three feelings on our Feeling Wheel that you are experiencing when you think about this situation. Remember, your feelings are real and you have every right to have them. Journal through them. Find the people and situations that you could forgive in order to have a better conversation with your boyfriend about how he can meet your needs to feel secure in your relationship. And forgiving is not about letting your ex's off the hook, nor does it give them free-reign to hurt you again. Forgiveness is about letting your heart free of them.
Now, what do you want from him? Assuming you want the relationship to grow in safety and trust, you will want to create a safe place where he can talk about his past relationship and what it means to him now. This is the best "affair proofing" you can do. So let him know the feelings you have had about this, where you are now and that you just want him to know and he does not need to take care of those feelings because you already have. If you can be clear about what you need, e.g. letting him know that you would appreciate him telling you when he talks to ex's, as well as how he is feeling about those conversation, and secondly how he feels about your relationship (making sure to use feeling words without a lot of story).
If you are tempted to press him or to repeat these concerns again (often perceived as nagging) then repeat the above process for yourself and try to be clearer about what you need. Also, check out our blog on communication!
Good luck and let us know how you do!
*You can listen to our fun time with Edina and Kevin here. Just follow the link: Wild 101. Enjoy!