Boyfriend is probably a big jerk. I'm an adult! Why can't I, should I ditch him?

Well, it seems pretty simple and clear to me. He is not the kind of person that is going to stand up to anybody about anything. He seems to fear any kind of confrontation and does not want to damage his relationship with his friend and wants you to understand that even though his friend did this to you. Get away from him, he will never be able to provide you with any kind of safe haven or sense of security and most likely will look to you for that for himself. He should be the first person to your defense and the one that understands the most about what you have been through. The only mistake you made is was allowing his friend to put his hands on you. Regardless of what he is studying, he is not a certified or bonded therapist at this point and he only used that as an excuse to get his hands on your body.