What happens when two of your friends (that you hang out w/ regularly) start going out?

The best thing to do is to let things play through and see what happens. Be there for them if something goes wrong and be happy for them if it goes right. Understand your feelings about being jealous or angry because you feel left out of the circle. When that happens you could try finding someone of your own you can develop a relationship with, whether it's in your group of friends or not. Often it's common for people who spend a lot of time together, and get close to each other to develop feelings. As for the PDA I've been there done that. You just have to turn the other cheek and if it gets to a certain level leave the room.