I think part of the problem is that happiness isn’t a permanent state and it’s knowing how often is too often for arguments that’s the issue. No relationship is perfect so how do you know when it’s too much?
I would have said that I was essentially happy with my XDP. He did so many lovely things for me, said all the right things, bought me gifts, took me on amazing holidays, rubbed my feet, we had fantastic sex. But if ever I was upset about anything he said or did he got very defensive and nasty and it always ended in (my) tears, often with him leaving and threatening not to come back.
Once the chaos was over I would miss him (trauma bond probably, but also because he was 90% a lovely man) and try to overlook the nastiness as just a blip. Because that wasn’t him that was his anger/defensiveness/inner wounded child/lizard brain etc talking.
It’s easy to separate the unacceptable behaviour from the person you love, because the worry about losing all the good stuff (and rightly so - it’s tough!) keeps you stuck.
It’s been the most horrendous year of my life since leaving my ex. I still miss him after many months and don’t dare speak to him or see him because I know the love is still there. For someone who has to see their ex due to shared kids or something it must be so difficult to end a relationship when you still love someone, even when they treat you poorly.
It’s easier to let the bad times slide and concentrate on the good parts, especially if you can vent somewhere like this and find validation that you’re not wrong to be upset by it.