My ex - thankfully this was a relationship I left many many years ago - made frequent insane accusations.
In addition to my day job, I worked part-time in the pub that he ran, and when his till was consistently short every night for a month or so, he accused me of being the one who had taken the money, because 'none of the other bar staff would do that'.
When I had to go away on a business trip for two nights, he told me I must be having an affair with my boss (a man who was twenty years older than me, married with four children and monumentally unattractive).
When I went for a drink with colleagues after work - literally for an hour - he accused me again of having an affair. I pointed out that it was actually only the women from the office who had been present, so after that he accused me of being a lesbian.
When I wanted to go to my brother's birthday drinks, he accused me of sleeping with my brother.
When I mentioned, purely in passing, that it would be handy to have an internet connection at home one day (this was in 1998, so home internet wasn't universal back then) he got incredibly angry and said the only reason I could possibly want internet access would be to watch porn. Then about a month later he spontaneously announced out of nowhere that he'd realised I probably wanted to talk to random men in chatrooms too.
When I was sexually assaulted by a stranger in the street - in broad daylight, quite close to our home - he accused me of, all on the same evening of a) inviting it, b) lying, c) only telling him about it to upset him, when I could have kept it secret, d) humiliating him by telling the police because now everyone would know his girlfriend was 'damaged goods', e) being at fault for 'not bothering to fight them off' during the assault and f) having an affair with a passer-by who witnessed the assault and gave me his number in case the police wanted to contact him for a statement.
Given that this ex was also violent and an alcoholic, I'm guessing you can see why I left him...