I can relate completely.
I went though a breakup in February of this year and it still feels fresh. We had been together for five years and were living together. We were very committed and loving to each other. The reason we broke up is valid but that doesn't diminish my love for him. He started dating someone a little less than two months after we separated, and it HURT. He seemed to be in a rebound relationship from what he told me, but it truthfully is none of my business how he chooses to live anymore. Missing him still hurts but I have come to terms with him moving on so fast. I came to terms that we all have our own way of dealing with things and although his choice hurt me, it wasn't about me. Personally I have decided to commit to loving myself rather than get into another relationship. When the pain of missing him is intense I find that exercising helps, it puts me back in my body instead of my mind and I can sweat though the emotion. I agree that avoiding contact is a great way to go to set up healthy boundaries for yourself. Although, I have a hard time setting those boundaries when he reaches out to me, and it always leaves me confused (so be careful of that I suppose).
Best of luck.