The agony of being the third wheel is a well-documented one. I actually consider myself to be a professional third wheel. A professional tricycle modification, if you will. If I want to hang out, I'm going to hang out - relationships be damned. Not everyone has such an agreeable position regarding hanging out with people who are involved. And I get it. There's the PDA, the inside jokes, the baby talk. It can all get pretty unnerving. But trust me when I say that it could be much, much worse. Tw…