It's a miracle you actually didn't leave the child's father before you even gave birth. You probably loved him so much, or you didn't see that you had other options.
Anyway, I would suggest that you tell the kid everything about his real dad. In this case, your child could make up his own mind when he gets older if he wants to be with his real dad or not. Keep in mind that he NEEDS to know the TRUTH. If his dad gets to him before you do, think of the possibility that you will be blamed (once again!) for everything that has happened. He has done it in the past, why wouldn't he do it again in the future?
I know you only want him to be a part of a family, but given the situation, I think that moving away from his crazy father is the best thing that you have done. After all, it is VERY possible that your child will also end up being like his dad because of the possibility that their background could be similar.
As long as you and your boyfriend would shower him with consistent love (see to it that you are not spoiling him!), then trust me, he wouldn't feel incomplete. I would also suggest that you try to make your child be surrounded by people who care for him and who love him, such as his aunts/uncles/grandparents, your real friends, etc. This way, he would grow up feeling secure and confident.
**My cousin is in a similar situation, but she had the wits to stay away from the dad after he hit her for the first time. Her child is happy because he feels loved by the entire family. (:
Thought he was 19... really he's 14