Oy, that's horrible. How did you end up seeing them on social media? I can imagine that would feed into depression. That totally sucks. Big hugs to you!

I do want to point out, they've moved on with their lives and is highly unlikely they're laughing at you at all. Try not to put your head in that direction. There's really nothing to laugh about.

All you can do now is cut them out of all social media accounts and believe in yourself. I'm not sure why your relationship fell apart but sometimes it's less to do with the individual and more to do with the dynamics itself. It just wasn't meant to be .. don't sell yourself short!

Keep your chin up. You'll move forward with someone new, as well (if you haven't already) and will not care about your ex. It just takes time.

Have you considered talking with a therapist about this?