Having a roommate can be a difficult situation to navigate, especially if one of you is third-wheeling. I know plenty of couples who live with one other person, and it can work if you're conscious about it. As the couple, you have to make sure you're not PDA-ing too hard in front of your roommate. And as the roommate, you have to assert yourself as an equal third. This balance can be tricky, though, as it can quickly feel like its two against one. But what happens when the couple is just doing…