Sheldon: Anyway, Tam stayed with her in Texas, and I had to move out here all by myself.
Amy: That must've been scary.
Sheldon: It was. I was lonely, and I thought I'd never make a friend again. And for a long time, I didn't.
Amy: But then you did. And great friends. If you think about it, if Tam had moved out here with you, who knows what your life would've been like.
[Montage of classic The Big Bang Theory moments with Tam as Sheldon's roomate]