<human>: Can you summarize the given text in a few sentences?

I thought my relationship with my ex-fiancee was perfect. He was the most supportive, giving, and caring person. Until I moved in with him. His personality completely changed. The smallest/most innocent things I would say would be twisted until I was somehow insulting him. He became controlling and tried to cut me off from my family. 

It was like a switch went off. I have no idea what set it off. I literally did nothing. We were planning our future and then one night he sandbagged me with so many problems and then twisted everything I said. Overnight he went from loving me to hating me. During the breakup he was/is the most vindictive person. I never suspected in a million years that he had this side to him. 

I can't help but feel that he played the long con against me. Being the picture of support and affection until I moved in with him and then everything changed.

I really want to learn how to spot these types of things. Has anyone else had this happen? Where a significant other changed completely and seemingly overnight? Can you share your stories? Tell me the red flags that you missed that you wished you knew back then. 

Also, tell me about the reddest flags that crop up the most in this sub. Or good books that can teach me how to spot red flags in relationships. I never want this to happen again and I clearly missed something. I'm hoping your experience will give me an idea of what to look out for in the future.
<bot>: Tell me your stories where your partner played the long con. What were the signs that you missed that you wished you knew back then? Help me learn how to spot red flags.