What is wrong with my ex? Is this a form of abuse?

Me and him have broken up and gotten back together for years, spending LONG periods of times apart during break ups. I always was dumb enough to take him back for one reason or another, and he would never acknowledge how much time has passed.

It would happen the same way every time, he would be charming and funny, before apologising for weeks begging for forgiveness about his head not being in the right place and he took it all out on me, he was depressed, I was the only girl to believe in him and he appreciates that. This would continue until I became friendlier to him. Then it would be perfect, always complimenting me, talking all the time, always wanting to see me, paying an interest. He's focused on life now because of me, he doesn't want to be smoking weed 2-4+ times a day. Nor does he want a night out of alcohol and cocaine every weekend now. He would tell me how he's starting to like me again and wants to be with me. It was amazing.

Until I would tell him that I liked him too. Suddenly my texts would be ignored all the time, if I mentioned it he would tell me I'm imagining it, I'm delusional and sensitive and need to stop stressing him. I'm causing drama. He wouldn't be interested in my life any more, I would be talking and he would full on cut into my conversation with a different topic about himself and wouldn't stop until I stopped talking and listened. When we broke up once he threatened me, told everybody he wants me in a coma, slandered me on social media, told everybody I was crazy, I honestly thought I was crazy and it was all my fault. He victimised himself to everybody as this decent guy and that I just started causing drama and getting obsessed with him one day. In his mind everybody was obsessed with him. He would ignore me for days, weeks before responding. Before ending us and cutting me off completely until he would come back again.

I can't go back down this road again but what is wrong with him? Is he abusive? Or something wrong with him?
What is wrong with my ex? Is this a form of abuse?
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