The divorce card when mad

My husband always threatens divorce every single time there’s an argument. I think that is not something that needs to be thrown up like that all the time just because of anger. And the thing is, he always gets angry due to his own self. He was diagnosed with ocd thoughts and bipolar so he always gets mad and brings up the past when he didn’t even know me. It’s not fair. I hate it and it exhausts/drains me. He doesn’t care. He stopped his medication and refuses to go back. He always talks about my ex from like five years ago and different irrelevant things. But the divorce crap is getting old. Why do men do this?!