Recently happened to me. What worked here was to really analyze why I was feeling so shitty about the whole situation. For me, it came down to a combination of my ego being hurt and me having a scarcity mentality. My ego was hurt because I felt she had chosen another man over me. I wasn't mad because I was dumped, I was mad because it made me feel like this guy was better than me. Once I had that thought consciously I was able to easily rationalize it away.
The scarcity mentality was me believing deep down that I had MY pussy taken away from me and I'd never get any ever again (again, this was unconscious). The solution here was just to go out and get some female interest. Voila, problem solved.
In the end I ended up reframing it in a very positive way. Remember all the bad times in the relationship? The ones that lead to your breakup? This guy isn't
stealing your girl away, he's taking her off your hands. He's doing you a fucking favour by keeping this crazy bitch busy so she doesn't get all up in your grill!
Plus from her snide comments it sounds like she's a vindictive little POS. Try not to waste your time worrying about what some she-devil thinks of you when there's a million nice girls (or naughty, if that's what you like) waiting around the corner.