Most Helpful Guy
That is way too hard to do but try to become a little colder inside, it sounds sweird i know, but coldness helps otherwise whenever you see him old flames with be lit again, try having a blank mind when you meet him and neutral expression on face, otherwise it is way to hard to face someone like that
Most Helpful Girl
despite the awkwardness, you might end up finding that pulling away is the best course of action. Explain the situation to your best friend and why you can't be around that other person that they're also friends with. Your best friend will understand and will help you as well. If seeing that person while you are trying to get over them will just be total torture for you, then you may have to be distant from them for a while until you can face them again.
Keep yourself busy, get a hobby or find new interests, if you like working out and haven't done it in a bit then go do that, go out and meet new people, etc.
Go and live life because contrary to what the die hard romantics think, life doesn't stop even when you have a broken heart.