My wife was like this all the time. It was so exhausting and I couldn't keep track of what she was mad about anymore. Then she started accusing me of cheating on a regular basis.
Then I found the texts in her phone to multiple other guys. Pictures and everything. I bent over so far backwards for her to keep her happy and that's what happened.
Dumped her ass, got a new girlfriend that is radically different (she communicates) and I'm getting my life back on track. Restraining order in place. The future will be good.
When someone starts accusing their partner of cheating out of the blue, it can rather often mean they themselves have been cheating and are projecting their insecurity about it onto their non-cheating partner. I'm sorry you went through that, but it's great to hear you're in a better situation now.