Please understand that your boyfriend’s past is his past and it should stay that way. Who he had sex with previously should have no bearing psychologically on your current relationship. If he had unprotected sex, then this should concern you only from the perspective of not wanting to contact a sexually transmitted disease but this should be your only concern. There is nothing that he can do to change his past. The problem is not his, it’s yours.
If his past bothers you, then it is important to examine why that may be. Part of it may be jealousy. Jealousy is related to a lack of self-esteem. If you felt fully confident about yourself, then you probably would not be thinking about his ex’s. You may also think that because he has had many sexual experiences that he is comparing you to those women.
Please realize that your boyfriend cannot change his past and it is not fair for you to be upset with him about actions that he took while you and he were not in a relationship. I also question whether it is fair to be concerned about his “friends” if he has not done anything untrustworthy to warrant your suspicion. With time and as you gain self-confidence these matters will likely not concern you.
In the meantime, it is important for you to recognize that these are your feelings and concerns. Your boyfriend cannot wave a magic wand and “wish away” his past behavior. If you want to continue the relationship, then you need to stop focusing on his past. Redirect your focus on the “here and now.” Judge him for the actions that he makes while he is currently in the relationship and do not punish him for his previous behavior which he cannot change. Try thinking of it this way. If it were you with his sexual past, would you want him to judge you as you are now or as you were then?