A years really not that long when you're depressed, and if shes snapping at him when he says something about it she probably knows how shes being. I dont know if OPs actually threatened to leave her if she doesnt get better, that probably hasn't really clicked in her head yet because everything becomes foggy. One years really not that long when you're spending your whole life with someone. Everyone will inevitably have a point in their life where they're not doing their best and putting a strain on their spouse for a significant amount of time.

I really think OP should start seeing a therapist on his own, maybe itll motivate his wife to do the same, and it'll help him work out the stress he has from her. It sounds like he hasnt put forth much physical effort other than just telling her how he feels. Maybe he should focus his words saying he wants to see her happy, not that she makss him upset. It might help her feel less attacked and more like he's there to help.