This is one I've been forced to think about recently.
To make a long story short:
*Edit: added spoiler code, because even in its concise form, this doesn't pass as a short post; following also contains (undetailed) references to an abusive domestic situation.
My dad physically abused my younger brother, and emotionally abused everyone but my older brother. His first diagnosis for depression was in 1987, when I was 2, and he's always refused treatment. He's passive-aggressive, right up til the point that he's just aggressive, narcissistic, and exhibits all the signs of classic attachment disorder. When mum (finally) divorced him in 2004, he also cheated her out of a bunch of stuff in the property settlement. The whole family breakdown thing was pretty traumatic (my younger brother was already unstable and very violent, and that got worse), and during the process he basically manoeuvred my sister and me into caretaker-style relationships with him. I couldn't deal with having such a dishonest relationship with him, and confronted him with my take on his responsibility for a bunch of things (including his abuse), at which point he rejected the possibility that I had any right to an opinion which differed from his (which is, of course, that he was the victim of terrible, oppressive behaviour).
Complicating the issue for me is the fact that several people (most people, really) either think of me as 'damaged' because of his behaviour, but also reject the idea that it's ok for me to cut him loose, since he's my dad and all. For several years, though, I could only deal with the most perfunctory contact with him, particularly since anything more involved than that involves stories about his new partner (he stayed with her family when he moved out of our family home, and 2 months later they ran away together; we have our own neighbourhood soap opera) and the farm he bought with the settlement money from mum - her superannuation.
My basic tactic with it is to remove the issues I have with my dad's past behaviour and he harm he's done from the immediate instance in which I'm dealing with him. Like your mother, Adelene, he refuses to admit that he's ever done anything wrong (my favourite argument: everything was mum's fault, 'cause she 'castrated him as a father'). All of these things are still pretty big issues for me. I really resent the fact that one of my parents put me in a caretaker position when he should've been looking out for me
. It offends every principle I have that he doesn't take responsibility for what he's done, and I still sometimes feel fraudulent when I respond to his affection as though I reciprocate it, simply so that I don't have to deal with the consequences of snubbing him.
The key for me has been in how I think about my own responsibility. Before I cut off most contact with him, I had to try to talk to him about all of it, for a couple of reasons - I had to feel I'd given him a fair chance, and I felt that I would be somehow complicit in his behaviour if I didn't show
him what he'd done. Every time I had contact with him after that, I felt fraudulent for not bringing it up, even though I knew how pointless it was, and how much it destabilised me. I don't intend to have any more contact with him than I have to, but these past couple of months has taught me that I don't have to be held hostage by the shit that he's perpetuated. He's failed to live up to my standards for basic human decency, and it's not my responsibility to change that. I'm also not going to get the outcome I want by constantly beating my head against the brick wall of his problems, so I'm finding other ways to deal with the effect he's had on my life.
Don't feel that you have
to allow the perpetrator of past abuse back into your life. Regardless of their relationship to you, you have every right to cut them loose if that's the best decision for you. Dead weights are dead weights, even if they happen to be your parents. Especially with family, though, I think it's often easier to maintain a low level of contact than it is to sever all ties, provided you can do it in a way that doesn't cause problems for you. If the only reason you'd choose to initiate contact is to get some kind of resolution out of it, it's worth reconsidering - the odds of a perpertrator maturing enough to be able to converse about an abusive history with even a minute degree of respect for your experience are slim.