I had one who genuinely believed that aliens built the pyramids and their spaceships were still inside them. He also had a 'spirit guide' who he would chat to. We would be in company, say, at a friend's for dinner, and he would suddenly say 'Ah yes, the infra red is vibrating, tell them to come through' or something equally random to mid air (the infra red thing is a direct quote). The guide was called Darren (over 6000 years old incidentally, who knew Darren was a popular bronze age name) and they used to have private jokes - ex would often crack up laughing for no apparent reason, except there was a reason, and it was Darren's wicked sense of humour. I was always told the jokes were too intelligent for me and I wouldn't understand them so I never got to hear them sadly. Ex was also obsessed with cleanliness and would insist I bathed twice a day and did spot checks to make sure I was clean enough throughout the day, if not I was advised to have another bath because the spirits wouldn't like it and my dirt would mess up lines of communication.
For someone so other worldly he clearly wasn't above the temptations of the flesh because the man was a walking fucking gland. I once found half a packet of condoms in his bag when he came back from a weekend staying with his friend and he quite blithely admitted that he'd had sex 'with a few ladies' but I had no right to complain because the fact he used condoms proved he loved me and didn't want me to catch anything from them.
Last straw was when he told me he was marrying a girl so she could get British citizenship, she'd have to move in with us so it looked real and they'd have to go on honeymoon. But it was ok, she was paying him £2,000 and I could have £100 of it to buy myself a treat.
I was only 18 and had not a clue about anything - I was new to London and figured I was just being terribly unsophisticated for not being cool with it all. We were together for two years altogether. I can laugh about it now, almost three decades on!