I think the whole reason he dumped her, if the spoiler is correct, is so that he wouldn't need to kill her later on. I already had this suspicion, so, if the spoiler's legit, it doesn't surprise me all that much? I thought either he was avoiding having to hurt her, or protecting her. Well, technically I suppose it's both.
I already kind of thought he'd kill whoever he needed to. This theory has definitely been floated before.
What I think we can take from this, too, is that what he has to do, he wouldn't even want an enemy to have to go through. He doesn't want anyone getting in his way, and he doesn't want anyone else getting their hands dirty doing it.
He may also be distancing himself so that he will be able to fight her when the time comes, if he has to.
There may be the possibility of killing him, as well, in which case he would not be the Big Bad, but we don't know who is. We may get to see him accomplish whatever his goal is (freeing the gods? Dropping the Veil? Both?) in the process, but only if we are able to actually kill him for doing it. Otherwise, he survives into the next game and we deal with him officially then.
As for the relationship being abusive... I don't really agree? I don't think that he would have been a romance if that were going to be the case. If he does end up killing your Inquisitor, imprisoning her, etc., I think that will be due to your own personal choices. I think it's pretty much inevitable that we're going to meet him again, because he's probably going to need the Anchor's power, and then it will be up to you if you want to trust him or defy him.
Those who say feeling sorry doesn't excuse his actions are entirely correct. And if he's willing to kill the one he loves for the greater good, well, that's a pretty monstrous attitude, but if he genuinely believes he'll make things better, well... one person vs. many? He'll choose many. And yet, it's also morally wrong, not just grey, to sacrifice an important part of your humanity no matter what greater good you think you are accomplishing.