"'ve got an abuse history too, and I know figuring out how and when to talk about it is one of the hardest things. I don't have a choice at a certain point because I have PTSD and sometimes it's more comfortable mutually for the other person to know why I don't react to some things the way you might expect than it is to just go into a flashback and give no indication of what's going on. It's hard for me but it might be harder yet for you since nothing has really forced the issue in 2 years.
Telling him now is probably the best thing you could do at this point. Making it simple might be the way to go. "I was abused and I have physical scars from it and I've been too scared to show you or talk about it. I know you love me and I don't want to be scared anymore so I'm telling you now, so that I can stop worrying about my past and enjoy our present and future now." "