A 12 year friendship. I don’t know what to do

How do you just end a 12 year friendship. Me and this guy have been best friends since we were 14. He’s been with his fiancé for about 5 years now and they have two toddlers. I noticed he is a horrible fiancé. For example he told me they were talking about their love languages and she told him hers was touch. He told me “that’s so stupid and boring”. He’s also always saying they’re never going to actually get married and just constantly down playing her. It’s almost her birthday and I’m trying to get him to plan something special for her but he says “no she ain’t getting anything but dinner because she lied about doing her taxes and is in trouble with the irs” I just feel like that’s a shitty way to view your fiancé. She hates me because him and I are friends but I really try to make him be good to her. Lately he’s been trying to flirt with me by calling me “hot” and “beautiful”. I just completely ignore those texts hoping he will see that it’s inappropriate. I have told him to stop before then he gets dramatic and constantly calls me buddy and friend. Idk I feel like I need to end this friendship because of the man he is being. He struggles so much with severe depression so I worry about him still. I don’t want him to do anything stupid since he has two babies.