I can only share what I went through with one.
I had 3 months of lovebombing, everything was perfect, we were meant to be and he wanted us to spend the rest of our lives together.
At 3 months and 1 day, a switch was flipped and that man disappeared forever. Literally over the course of a 2 hour journey. When we set off he was loving, fun, engaging and great to be with. When we arrived, he was cold, distant, condescending, wouldn't look at me, touch me, communicate with me or spend time with me.
Took great pleasure in ruining things I worked at/for. I spent hours shampooing/cleaning his living room carpet, he deliberately dropped a full cup of coffee on it the next day, and he made sure I saw him do it. I'd cook a nice meal, he'd wait until I was near the bin and scrape it all into the rubbish, making sure I saw that.
I couldn't do or say anything right.
It was hell.
I tried to ask what was wrong but he'd just shut me down.
Id ask if he wanted me to leave but he said we loved each other so I should stay.
I left, 3 months later he started hoovering me back, saying how much he missed me and he wanted to try again and he'd be better. He wasn't.
His phone was never out of his hand. He was on multiple dating sites, chatting and arranging dates whilst telling me I was "the one". A friend saw him on POF and tipped me off so I set up a profile and catfished him.
The thing that gets me most is that with the benefit of hindsight, he has absolutely nothing to offer any woman but carries on as if he's the catch of the century. He's a fat, scruffy, sweaty, sweary 55 year old with no qualifications, no trade or profession, has dubious dental hygiene and a house thats falling down around his ears. He's actually very boring.
His family were all lovely though and tried to warn me what he was like as they'd seen it all before, several times over. He's fallen out with all of them now too.