Bipolar fiancé

Hello. I’ve been with my fiancé for 5 years and he is bipolar. We have a nine-month-old daughter and we hardly argued in the past but lately he’s just been so on edge and so snappy yelling in my face, picking fights with me over stupid little things, threatening to end our relationship if he doesn’t get his way and things like that. I work in mental health so I know a good amount about bipolar but I’ve never seen him like this. It’s just the last few months that he’s just getting worse and worse and he won’t get his medication checked and he keeps forgetting to take his lithium. I’m just looking for any advice on ways to help him or ways to help myself. I’ve tried to sit down and calmly talk to him but he just ends up getting even angrier at me. I’m at my breaking point, I don’t know what to do anymore so any advice would be great