Telling my boyfriend I was sexually assaulted in college

My boyfriend and I have been dating for about three weeks now. (He's 30, I'm 23) We've been taking things very slowly, going on fun dates, and having a good time together. Things haven't gotten very far physically, just making out for now.

Confession time: I was sexually assaulted my senior year in college. I went to therapy for about six months after, and I'm okay now for the most part. Sex is still difficult for me, I usually detach emotionally and find myself "zoning out". I've only told two people besides my therapist about the assault. I feel like this part of my past is something I want to share with him, but I don't want to scare him off with this baggage too soon.

Should I tell him? If so, when?