Maxine,
Your b/f is scared of pregnancy for a million and one reasons not the least of which are because you're both young and his csa issues. I'm glad to hear that both of you can talk about this and take steps together to avoid a pregnancy and calm the fears that arise because of sexual intimacy. That's a very mature and wise thing to do so you should both be proud of yourselves for that.
As for how he can get past his fears, well, I think that will only come with getting older and maybe seeing a therapist. I know if I told my b/f I was pregnant he'd panic. So would I at this point in my life.
But really, we did talk about it in the beginning of our relationship. I already had a child from my first marriage but he never had children. I was very content with the fact that I'd reproduced myself and I was all done, but what did he think? Well the answer I got surprised me. He told me I didn't need to worry about him ever wanting children because he knew he'd be a terrible father and the last thing he wanted to do was put a kid through that. This sounded completely crazy to me; not that he didn't want kids, I was more than fine with that, but his reasoning was all messed up.
I didn't know about the csa then. When I found out about it, I also found out that my b/f believed the myths out there that if you were abused, you were bound to abuse yourself. He was terrified of that happening and vowed that he'd never have children. His therapist and I are working very hard on different fronts to convince him that this myth isn't true, but it's still a very real fear for him.
Your b/f may have the same fear for himself and future children but not be willing to admit it. It's a horrible thing. I know my b/f would never harm a child, the exact opposite actually, he would protect them with his life, but he's frightened anyway. If this fear is playing at the back of your b/f's mind, I can only imagine the amount of anxiety he feels at even the possibility of an unplanned pregnancy.
There is no quick, easy, absolute fit answer to any of this stuff. Is your b/f in therapy? would he consider it? If not alone, the the two of you together where this could be addressed?
The only advice I can offer in the here and now is to keep doing what you're doing. Keep talking and being responsible.
ROCK ON..........Trish