Soleq
I would honestly suggest seeking professional counseling. Feelings of guilt unfortunately usually follow sexual assaults (the "it's my fault because I let it happen"), and only through time and professional help can those wounds be healed. It doesn't surprise me though that it's taken you this long to realize what has happened. The mind blocks harmful things until we are ready to deal with them.
I agree with Soleq. Although he did say that it's sexual assault it's still considered rape, or a form thereof. Even if you didnt have actual intercourse you still had a kind of sex with him unwillingly. You said no and he continued. Regardless if it felt good or not.