Why is he acting like this? Is this some sort of manipulation?

what do you think is going through his mind? is this manipulation?

my ex was 21, and I was 14 when we dated. he forced my mouth onto... then was apparently cheating on me the whole time. the girl he was cheating on me with, he is in a relationship with. he's tried to cheat on her multiple times with me. I always tell him no and tell him to leave my alone. exactly a week ago, he was at a family event (he's a close friend to my family). he kept messaging me while he was sitting next to his girlfriend. after the event, he messaged me saying I looked so beautiful. I told him off and said this needs to stop. he said he understood and it would never happen again.

anyways, just yesterday I posted a photo on my story. it was with my family and myself. he replied to my story saying "you look good in black". I got upset and one last time, told him to stop. I said to him that he needs to respect his girlfriend. he then said, "I was just being nice". I said, "I know. but still". he then got really defensive and was saying things like, "I thought you wanted to be civil". he then lastly said, "You've made it clear that for us to be civil is no more talking". and he really rude with it as well. I don't know why he's acting like this. who goes out of their way to compliment their ex? especially after the discussion we had? why was he acting like that? why was he so rude about it? What is going on with him?
Why is he acting like this? Is this some sort of manipulation?
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