[Always *]

I'm sorry your ex is dating someone you don't like. I hated the girl my ex started dating too, she was totally crazy and really bitchy and the kind of person who'd jump and beat up someone she didn't like just because she didn't like them and smoked weed etc. I was mad; why would he date someone like me (smart, classy, nice) to someone who as rude, belligerent, had no class, and took part in illegal behaviours? I was insulted. It was made harder because I questioned what it said about me.

What helped me was finally accepting that I can't control anyone's choices but my own. My ex is my ex for a reason and, well, good riddance because clearly he's a lot worse than I thought if those are the sorts of people he's attracted too; it's not just about romance too, if that's who he's willing to date, then that's who he's willing to be friends with and, sure, he might surround himself by some good people such as myself but it doesn't change the fact that I don't want to be around someone like that. I think that accepting that I don't need people like that in my life really helped.

I don't know if anecdotal experiences are what you'll consider helpful. But maybe that'll help you in framing your own rationale.