First of all, you are so courageous, and it is wonderful that you want to help your boyfriend. You are correct that you can't be the one to do it, but you can, of course, steer him toward some folks who maybe can help.
Smart people DO have a difficult time dealing with their issues. I know both from personal experience and from knowing a lot of other artful dodgers! (He would need to find a therapist who is as quick - or quicker - than he is...and they do exist.) There is, I believe, a tendency among guys to intellectualize rather than be in touch with their feelings...or at least to intellectualize in the expression of feelings. It's a guy thing. On top of it all, if there is, in fact, any abusive, shameful, or disturbing stuff rattling around inside, there is a natural tendency to keep it well guarded. That's how we survive.
As you suggested, it sounds to me as though Jeff may be a victim of his uncle's abuse. But as someone who stuffed this kind of abuse down inside for almost fifty years, he isn't going to disclose this to you - or himself - over coffee some morning. But the fact that he is able to acknowledge that his siblings were abused - and that he MAY have been as well - is a crack in the door.
My wife of almost twenty-eight years has been a wonderful support to me...particularly in the last couple of weeks when I finally "got it" that a lot of my life-long behaviors can be directly linked to sexual abuse that occurred when I was not quite five yeas old. She loves me unconditionally, and in no way has she made me feel shameful or dirty or perverted. She has been a steadfast presence in my life and, I think, it is because of the fact that I now feel "safe" that I am finally able to confront those demons....
It appears to me that you love Jeff and that you want to continue to have a relationship with him. In my opinion, knowing this (all the way down to his toes!) is something that will be of enormous comfort and relief to him. But my advice would be not to communicate the message that you think there's something "wrong" with him and that to be in relationship with you he's got to get "fixed." He can recover and become healthier and lead a wonderful life, but from my experience, you never get "fixed," but you do get better.
There must be some wonderful qualities about Jeff that you see and which have attracted you to him. At some point, you may wish to suggest to him that - in addition to individual therapy- you'd like him to go with you for couples therapy. Not with the intention of fixing him - or you - but with the idea that understanding each other's background, family of origin, and "baggage" you can move forward together.
This web site and discussion forum may also be helpful for you both. It has helped me a great deal to discover - much to my amazement - that there are a lot of guys out there like me who are struggling with issues that I thought only I was dealing with and keeping repressed. If you wish, you have my permission to print out this response and give it to Jeff when the time is right.
Hang in there...there's lots of support here.