I question anyone who doesn't see a 6 year relationship as something inherently worth saving... And to be clear, I explicitly disagree with the notion of "abuse" and "abuser" being applicable to this case. I have opposed it from the outset. If I happen to concede that this person is abusive, don't worry, you'll be the first to know about it.

Why? There's just nothing to suggest this person is acting with malice aforethought. There's nothing to suggest psychopathy, ASPD, manipulative behaviour generally. OP said it herself: he's a great guy. Nothing at all in what we have before us suggests this behaviour is premeditated or abusive.

On the other hand, there IS evidence to suggest post traumatic stress or problems with relation to the father during childhood. The explosive outbursts of anger when the sense of identity is threatened, the fact it's confined to the familial or spousal relationship, the classical "0-100" followed by a period of cooling down. It's all pretty textbook, really. Of course, I've still implored OP to solicit a psychotherapist. There are also no guarantees it will work. And so on.

I'm afraid this will be the last time I reiterate. I hope I've made my position clear.