I didn't really mean this thread to turn into a comprehensive review of my family life, but I'm glad it has, and I really appreciate all your comments, and the fact that so many of you have obviously given it so much thought.
As it happens, the last couple of weeks have been a bit of a crisis point for us, and yesterday i even had my father on the phone, saying in the most supportive way possible that he thinks I should walk away.
However, a combination of factors, including the tough love advice I've had on here, have I think hardened my attitude. I think DP senses a change in my approach. He knows that I've detached from him to some extent, and that he's pushed me to the point where it wouldn't take much for me to go. My attitude now is that I live my own life and if he feels like being involved then he's welcome. DD and I won't wait for him - we'll enjoy the fun times with him, but if he's not around then we'll just have fun times together and with our friends. He's the loser in that case.
I'm not going to give up yet. You must believe that I honestly don't think I can single-handedly save him from himself. In fact, I'm now abdicating any responsibility for him. What he does with his life is his business, but I want certain chores done before I get home each day. That way, I feel less resentful and DD gets to see a slightly more balanced division of labour.
I am the child of divorced parents, and I've effectively had 4 step-parents in my life. Three of them haven't been bad, and I know that most step-parents are loving, caring people. That said, I know what it feels like to be in that situation, and it's not always great.
Before I give up on this situation I want to know that I have given it my absolute best shot. The difference now is that I have timescales in my head, during which time I need to see significant improvement. It's not an easy choice, particularly since I know that I'm worrying both my parents. But I am financially independent, so I know I can walk the minute I'm ready.
To those of you who want me to get straight out - you haven't persuaded me, but you really have strengthened me. thanks.
(Blu - they were using paint-stripper, which was asphyxiating us through the floorboards.)