Barney sighs. How could Larry not have noticed this?

"Look, it's like this. You're a couple. A couple is two people. It's not like we're the three musketeers or whatever. There's you guys, and then there's me. I feel like a third wheel and that you guys are going to go off and get married and I'm going to be left behind..."

And he was babbling. He'd had too much to drink and now everything was coming out and at least he'd stopped himself before he got to the part about Ted dying alone, eaten by cats.