How to deal with them: They're going to drag you down to the bottom of the ocean, and you'll end up miserable and friendless. Get into another relationship (or faux-relationship) fast and plaster as many pictures of yourself with your new guy or girl on social media. Best-case scenario, it makes them go berserk and they move to Slovakia or something.
The one who's still friends with all your friends
Ah yes, the eternal struggle of keeping the friends your ex was friends with. The problem is, the ex in this situation isn’t usually that bad, hence the stubbornly enduring friendships.
How to deal with them: This isn't the end of the world. In fact, these kinds of relationships are salvageable. If you guys have the same friends, then it's pretty likely that you have the same sense of ideals. So, just talk about it and figure out a way to make it work. Maybe, through being friends, a new spark will ignite some white-hot passion. It's not without precedent.