My sexual assault is affecting my boyfriend and our relationship

Almost two years ago today (a week after my boyfriend and I hadbrokenup),Iwas sexually abused at a drunken college party by someone I knew. Despite the break-up my (ex) boyfriend showed up at the party where he found me passed outin the bathroom and carried me out. After that week we remained apart and went our separate ways. We never discussed what happened at the party, I never sought professional help, and finally let go of my self-blame and guilt after weeks of confiding in friends and over the last couple years. Three months after the event we got back together, almost 1 1/2 years ago now. Our physical relationship has never been quite the same. Just a few days ago I confronted him about this, as I have before but this time I demanded to know why he didn't have the same desire for sex, even if I didn't want to hear it. I never thought he would've brought up what happened at that party. But he told me that after finding me in the bathroom and hearing what had happened to me, he has always felt guilt for not getting there sooner and anger at the guy who took advantage of me. To him the event replays in his head whenever we attempt any kind of intimacy. I really have no idea how to help him. I've been able to work through my own emotions and fears and reactions with the help of my friends. But he's never moved passed what happened and has let it affect our relationship unbeknownst to me for a year and a half now.