You will probably need to speak to a therapist in order to get to the root of your issues, particularly with what may be repressed memory. I am no therapist but if there was abuse, it's not a matter for just casual friendly (or anonymous Internet) advice -- it's a matter for a professional.
And no, it's not a pity party. Don't worry about that -- if it indeed happened, then it's something you've got to deal with. Nothing pitiful about that -- in fact, it's a strong position to deal with your past, whatever it might be.
As for your partner, I imagine it's a difficult subject for him to broach which is why he's silent on the matter (how do you know he was abused? Did he tell you that much at some point, or did you hear it from someone, or infer it?). Saying that you understand is, well, it's not productive and probably not the case. Even if you both had identical experiences, it doesn't necessarily mean a shared understanding or a shared reaction. It doesn't mean you can't be loving and a good listener. I think the sentence, "You can tell me anything, and I care about you and I will do my best not to judge
." is one that should be said in any and every relationship, regardless of whether anyone's been abused. I'd say that, or a variation of it. If it leads to him opening up to you, fine. If not, that's also fine, too. You got the message out, that you're a safe person to talk to.
Now, as for the changes in your behavior, appearance, etc., I don't necessarily think it's self-destructive but recognize that, sometimes, we change ourselves for the sake of trying to please the people we care about. That's not, usually, such a great thing to do, over time. Losing your own identity in someone else is a recipe for eventual resentment. Be who you are - and you might not know the details of that, yet. But don't be who someone else thinks you should be.