Partners multiple personalities

My partner and i have been together for 4 years, we have 2 young children. It has been up and down throughout the years which i assumed was due to his depression. He goes through stages of being horrible, nasty and flat out rude but as soon as i feel myself getting to a point where i cant handle it anymore he switches and becomes perfect again. These switches keep happening like once or twice a month, lasting different lengths of time. He has made jokes saying his bipolar knows when im about to leave.

Im struggling with waiting for the next switch but also fighting with myself whether to stay or leave. There are beautiful qualities about him i love but theres also a really dark side to him. I feel so guilty to leave in case its his depression but he flat out refuses to get help. He knows the issues, he knows its his moods causing our relationship to be up and down.

I'm at a loss