I need a kick in the butt

Now that I found out he has himself his first real girlfriend that is 10 years younger than I… he is 28, I am 30. I can’t help but think he has changed. That last sexual contact I had with him was 6 months ago, which ended up being the icing of the cake for me for sanity’s sake. I have reacted in rage, anger, tried to get revenge, etc… every time I saw him since which was a few times. Last time I saw him was at my brother’s jack and jill and he met this 19/20 year old there, and they are now an item. They have been together for 2 months hence 2 months NC for me… she is popping up everywhere on facebook with mutual friends. I know I am being irrational, and extremely emotional, but I need reassurance….one like him cannot change in a span of 6 months, right? One who has abused me, lied to me, manipulated me… which I all allowed of course… but he really didn’t change, right? He is just changing his tactics, and going for weaker prey such as innocent 19/20 year old, right? Who I feel bad for… and will end up being a shell of her pretty self. I just keep going back to that false belief in my head that I wasn’t good enough. I can’t shake it. This is a whole new hurt for me. I know many people on here deal with this similar situation. I need advice. I need a kick in the butt! I keep on going through highs and lows. One minute I am fine, and the next I am balling my eyes out. This is a thing that called me a cunt, whore, skank, asshole, bitch… usually after sex, lied to me, said I had no real friends, that I disgust him, begged me to see him, told me he loved me, amongst other crazy, scrambled egg bullshit. He did not change in a span of 6 months, right?