I would use that as an opportunity to concentrate on what I could do to improve my own happiness. By making an effort to practice hobbies I want to get better at, by looking up movies I want to watch at least once, and by keeping myself busy. If you have a lot on your mind, you probably won't have time to deal with that sense of loss. However, if you were forced to confront it, there is no other option but to embrace that sadness. The fact is, if you feel like you made the right choice, you won't be dwelling with regrets or what-ifs. However, there are some situations that are better left rather than trying to fix. Everyone has their own pace, has their own way of recovering from that sadness. What I said is only some of them, but it’s entirely up to you how to overcome yours.