I have a lot of sympathy in your situation.
An awful lot of abusers have been abused so your case is not that rare, not that there is much solace in that....
I feel all you can do is to let him know that you are there for him whenever and if he wants to unload. I certainly wouldn't go out of my way to meet your old friend. Also, I am sure, as has been suggested, a support group can also help you in your feelings as I suspect you are feeling guilt and shame that this has happened. That is a natural parental feeling.