This is just my take on it. Everything is summed up here in your own words.
"So in a very heated argument. I'd pretty much always win. "
No guy likes to be emasculated by his W like that. You say that you had past issues with depression, grief, etc. Well rather than dealing with it in a healthy manner, it seems like you took it out on him. And rather than arguing with you, he took the lighter side and let you 'win' because he knew no matter what he did, you want to win. Even though you say that you want him to argue back, etc. you still want to win. So why would he want to go through all that drama for you?
Now I'm not saying that he didn't have his own faults, but it sounds like he just got fed up. How have you shown him that you're not that same person any more? Can you honestly say that you won't treat him the same way anymore? He, like any other guy, just wants to be treated with respect and dignity from his W.
M-43 W-40 2D - 9 and 5
Emotion, yet peace. Ignorance, yet knowledge. Passion, yet serenity. Chaos, yet harmony. Death, yet a new life.
