My boyfriend told me something about his past that really bothers me?

My boyfriend and I were having a heart to heart and he told me something about his past that really bothers me...it's really twisted. He told me that when he was little (like 10) that he and his first cousin used to "play" with themselves. And they are still really close now. And that just seriously freaks me out. But he knows a lot about my past, like that i've been raped and i used to cut myself, and he hasn't judged me...but I can't help it...It just seems soo wrong to me. God I don't know what to do...someone PLEASE help me!!!