Firstly, anything I say on this subject should be viewed as suspect as I have such a terrible history with relationships, but here goes anyway….
OP – I agree that generally it is very rarely just the fault of one party. However, if one party does decide to be abusive for whatever reason, it is easy for the other other to fall in with it (rationalising it as something minor until it’s accepted behaviour) and not stand up to it, I know I did. I got on tolerably with my first wife, but she could be a real demon and was certainly abusive in putting me doewn in front of others and with rages and occasional violence etc. She went away for a “weekend” with the office sleaze when I was away at a pre-agreed stag do, and reacted in fury to my somewhat indignant questioning when I found out where she’d been. I was too feeble however to issue ultimatums or whatever though at the time, and stupidly “let it go”. I do however still feel tremendously guilty as I was the one who ended it, although I still feel it was the right thing to do. Second one was a rebound, but she seemed (initially at least) to be a good friend and much better adjusted than the first one (if she kept off the sauce, sadly that was rare). How wrong could I be though…..she was off to have someone else’s kid within a few years and I now see just how manipulative she was. I was totally devastated when she left without warning after telling me it had been going on behind my back for a while and I pretty much gave up for a while.
I then resolved not to marry. Had a good time and basically learnt that everyone has faults, don’t put them on a pedestal, adjust to their flaws or walk away if you can’t etc. Then I met Mrs Ononeorange, and was so knocked over that I ignored my rule on non-marriage. I know now what a relationship founded on equality and mutual respect is really like, and couldn’t be happier.
I rationalise the above as me having learnt the hard way what most people learn when they’re in their teens, but I suppose the “moral” of this shameful story is the bit about mutual respect. I also realise that not having had any kids makes the decisions etc much easier.