Hi hayley. There are two things that stand out to me here. First, you say that your boyfriend is constantly more or less pushing it on you, and finding ways to always change the topic back to sex. Then you mention that you've been accused of sexual assault. Those are two pretty serious things and, not that you need a reason, but may have quite a bit to do with why you are really not feeling into being intimate with anyone. But I think it is more important to remember that you don't need a reason not to be intimate, and you don't need to feel bad about it, or like something is wrong with you. There is nothing wrong with you. You just don't feel like it. And that's perfectly okay. And the more pressure you put on yourself, and the more pressure others put on you, the more you are going to keep stressing about it and the more it is going to keep getting blown up into huge proportions. It's your body and you have sovereignty over it.
Which brings me to the boyfriend. I think it's time to stop being nice. Clearly this person is not respecting your attempts to divert conversations and is not hearing your requests for him to stop. I think it's time to tell him to either shape up, or ship out. You don't need that. And I think, probably, the same goes for the friend. Let her know that you're not into it and would like to talk about other things and that if she can't handle that, maybe you need to spend less time together.
That's my two cents. Please don't feel like I'm telling you what to do; that is absolutely not my intention. Take what you like, and what you find useful, and leave the rest.