Oh, I feel you, your body hurts with the heartache, there is a permanent lump in your throat, everything you watch or listen to reminds you of something, and the urge to see them overrides everything. Heartache is a bastard, and we've all been through it, but most of us have survived it and come out the other side better for it.
Please don't beat yourself up over the why's and why not's. don't question what YOU did wrong, just accept that you, for whatever reason, are not right for him. You HAVE to because any further attempts to try and understand will only make things more difficult for YOU and if you chase him, will make him run away further
I PROMISE you if you can somehow get through each day, or even hour, eventually you will feel better, you will become angry and realize he's a selfish shit and as you said, he could have done this in a respectful way but instead did the cowardly thing and ran.
As I have done, and millions of others, you will look back at this time and wish you'd spent less time wondering about why and more time doing whatever it takes to move on and away from a man who is not only a malignant milksop but truly not worthy of you