Just wanted to say we have been through something similar.
Our boys first dad was abusive, neglectful etc. When we finally got direct contact with him (4 or more years ago when boys were 9 and 8, adopted at 3 and 4) at first initial contact was with us. Then he started writing letters addressed to the boys directly (of course, written to me to pass on to them as I saw fit).
He has #1) taken full responsibility for what he did #2) apoligized over and over again. #3) offerred some sort of explanation for his behavior that wasnt excuse oriented, but did show that he loved them, tried his best, but his best was not good enough and lots of that was based on his own childhood. #4) is supportive of their position in our family
He actually did this to the point that I had to write him and say "ok, we understand you are sorry, NOW MOVE ON PLEASE"
I would love letters that were chit chatty -- now all he wants to do is beg them to love him again and how sorry he is.
Anyways, I think there is NO problem with you having those boundaries.