What do you think this is?

I've never experienced this with any other person in my life. My friend is constantly getting angry with me over the smallest things. They'll then start a fight, continue the fight, tell me they're never talking to me again and block me on all social media, never apologize and then not talk to me for 2-6 days, ignore my texts. Then suddenly text me again, readd me and act like nothing happened.

It's making me go crazy because it happens every two months and I tell them it is messing with my mental health and I don't understand if they want to stay friends or not and they'll not say anything. They'll just ignore me saying that and continue to treat me VERY WELL until the next blow up about a month or two later where they do the same thing.

I can almost guarantee they'll go off on me again and tell me we're not friends anymore blocking me on everything in a few weeks. It happened so many times. Last time they were mad at me for saying fish is healthy. They're vegetarian but they expressed wanting to try chicken so all I said was that's cool you could try fish too I know some great dishes and they said fish isn't healthy, I said yeah it is and they started EXPLODING on me with a strange attitude and it got crazy. They'll then say "stop forcing me to eat fish" when I casually brought it up for the first time.. and then they'll say "you're manipulating me to brain wash me into doing what you want, that's abuse you're abusing me you're a psychopath" etc it escalates.

I don't know if it's bipolar disorder, multiple personality disorder, borderline personality disorder or what. It's really strange behavior and they're usually very polite I mean they're genuinely nice when they're not doing this and that's why I'm friends with them but then they turn evil.