He broke up via txt message? Commitment and intimacy issues on his part most likely.
But, that's vague, like your details... Pretty much you have to learn to be OK with people leaving in which you get no closure to the relationship. Which sucks, but as with anything it takes time. You could go sleep with 3 guys to drown yourself in brain chemistry to feel good, but it's emotionally hollow and I would recommend against it both for health and sanity reasons.
Pretty much you need time, support from friends, and to do your own thing.
"Well, then," the Cat went on, "you see a dog growls when it's angry, and wags its tail when it's pleased. Now I growl when I'm pleased, and wag my tail when I'm angry. Therefore I'm mad."