I am a believer in the “No Contact” Policy after a breakup. Breaking up with someone you invested time with and shared time with and adored is a loss. Loss like losing a loved one to death needs time to grieve the person you lost. Moving forward and going through the hurt and emotions that you feel is necessary to moving forward and being with the person you are meant to be with.
Your ex appears to be pretty fickle when it comes to relationships. Jumping into relationship to relationship appears that the relationships didn’t mean much to him or he doesn’t want to feel the pain of loosing the relationship. If the relationship didn’t work out than it wasn’t meant to be.
I understand that this is probably pretty hard to hear right now but everyone goes through this at some point or many points in their lives. Learning from the relationship mistakes is necessary to improve when you are ready to move forward into the next one.
Keeping yourself busy and doing some things with your friends that you enjoy is pretty helpful. Eating healthy and exercise regularly helps to ward off depression because it acts like an anti-depressant that increases serotonin in the brain.