It sounds like he has a pattern of hurting women and that is hard to change. That is why you feel that trust is an issue. Trust should be an issue in this case. He has to learn how to be in a relationship and he hasn't done that. All of his cheating has avoided a healthy relationship. He has proven already that he doesn't know how to function in a healthy relationship. You can model that for him but if he is going to destroy trust it won't work. He has to be 100% totally committed to a relationship. You have to decide as the partner if that is possible. He's says you are different but he has to show it in his behavior. Words are cheap!
Trust is going to be an issue for quite a while. However if you think it is worth it to pursue this relationship then things could work out. You could have a short stay with a couples counselor to help you both commit to this. If you prefer self help then get the Mars and Venus series for communication.
Talk to him about what he needs to get it together. Decide if that is possible. Consider that you are very young but if you want different things. He has to want it
Please press accept; this is the only way I am compensated
Then he has some work on self esteem to do. You can't do that for him so it will be difficult to address him. He needs to see a therapist so that he doesn't personalize everything you say. He is going to feel that you are putting him down if he feels like a horrible person. If you are insecure as well then you may think he is cheating because you are applying your own thoughts to a situation. He may benefit from a therapist and the therapist can bring you in to process your insecurities or his cheating so that you can both communicate better.
Please press accept