yup, this is the right place to vent unhealthy feelings which probably wouldn't do much good if shared with indiscrete friends. Kudos for spitting it out as frankly and unadorned as you can.

Your obsession is just the symptom, not the cause of your situation. You could not have been with this guy, since you were not interested in him. The fact that he is happy now is inconsequential, like you say. The only thing your obsession is useful is as diagnostics: it tells you are unwell.

The way you solve this is how you would solve it if it happened to a friend of yours: go get a boyfriend. You'll forget about them when you are busy with your own relationship ^_^ Actually, perhaps they can return you the favor, and present you with to nice guy?