Having a hard time right now

I have been having a really hard time lately. It is a major emotional set back. I am divorced from narcissist after being separated for a year and a half. A month ago, after receiving final divorce papers, ex made known a new relationship with a new girl. We are both 38yo. The new girl is 22-23yo and very beautiful with 2 kids of her own. I have not been able to take proper care of myself over the years because I was married to a narc and before that a single mom to his child. I am also not interested in getting into a new relationship anytime soon. I am feeling like crap because he left the state with her, where he can get work, has family and friends to help him out, and taking care of this new girl and her 2 kids while leaving his 3 behind with me where I have no support. I tried to get away from him years ago but he wouldn't allow and after putting us through hell since then and destroying relationships, he just picks up and leaves to start new life with this girl. I also wonder how a man that ugly inside can manage to hook up with a young beautiful girl because I can imagine what he's thinking. "I got this young hot girl, she appreciates me.....I can't be half as bad as my ex wife says I am" Please help me. The self esteem I regained during separation is fading fast.