Discussing sexual fantasies with a male partner can be tricky sometimes, because some men can't handle a woman having sexual desires other than vanilla type thoughts. Not all men are as well understanding when it comes to "their" partner being sexually abused, and it can be a turn off. Realize this is "their" problem, (as far as the negative attitude towards what has happened to you) not yours. What happened to you as I hope you realize was absolutely not your fault whatsoever.
Discussing the abuse that happened to you when you were young is something you should discuss with him only when you are ready, and you are at least kind of certain your relationship is strong enough, and he is open enough for you to be able to discuss it. Again, not because of you, but because of what his attitude might be, as far as being understanding towards it. Once you feel you can discuss this type of thing with him, it may very well help in him understanding what has gone on with you, and why you feel the way you do.
First, if you haven't felt your past is something he could handle at first, you should have just a general talk about sex with your boyfriend and see where he stands in all these issues, and get the feel how he would react. Try and get him to discuss some of his own sexual fantasies first and then that will at least give you an idea where he stands.
Once he is able to talk about some of his, and if any of them are in the direction of what you have an interest in, then go with that in maybe a role playing activity, and then maybe you could expand on how it might be more exciting. This could lead to a time when you might feel more comfortable in talking to him about your past, and what desires you have in fulfilling your fantasies.
Fantasies are just that. They are something for playing, and not necessarily something you would want to act upon in real life. Sometimes one does act on them, but I must say to be careful if you do, as many relationships have broken up when fantasy becomes reality and one is not prepared, or ready to take it to the next step.
I hope this gives you at least an idea of how to start a first step. Good luck, and great sex! Keep us informed how things are going, as it may very well help someone else having the same type problems.