First of all, don't apologize for asking this. Reaching out for help about something that you are uncertain about is always a good thing so don't be sorry about it. And if other people aren't comfortable answering it, it's not your fault. It's simply because they just don't know what to say and that's perfectly fine on their part too.
Okay so now to your question. Right now I want you to think about what outcome do you want by telling your boyfriend this. Do you want him to then take things slower, help you get comfortable, and/or is it just for the sake of him knowing? Determine this first before doing anything else.
So if you want to try to keep it casual, what you can do is bring this up the next time you are alone. Just start off with saying that you want to talk to him about something. Then go straight to it by saying that as a child you have been molested and being intimate is something you aren't used to. After that tell him what you want him to do to accommodate this. If you want to make this more official or just tell him at a certain place or time, then do the same thing except this time tell him in advance that you want to tell him something. Just remember that you shouldn't beat around the bush and be direct. You don't have to tell him what you don't want to tell him but be prepared for him to ask questions and have some answers ready that are civil and calm (such as, "It's not you but I just don't feel comfortable talking about that right now because it brings me bad memories but maybe in the future" as compared to "It's none of your business!").
Your boyfriend should understand where you are coming from with this. If he is being a jerk about it by thinking it's all about him or something like that (such as being offended that you're uncomfortable with getting intimate because he thinks that it's a direct attack or accusation of him when really it's not), then he is immature, selfish, and wasn't even worth it. If he is a good guy, he would try to empathize with you and help you the best that he can. So I know that revealing something like this to someone you like can be intimidating but rest assured knowing that if that person is truly a good person, they will be supportive.