You’re unhappy because you can’t let go of the past. You can’t let go of people and accept that their life is still continuing without you. It’s hard and it sucks, but you have to let it go in order to become happy with where you are right now. People change and you also changed — it’s inevitable. In order to find happiness in your life now, you need to stop holding on to something that’s long gone. Perharps nothing last forever.