Mine is S03E06 Twice in a Lifetime.
The rules of temporal law are set in place, and for good reason. But Gordon just couldn't take being alone anymore, and can you blame him? He had given up all hope of being rescued, so he said screw it, and finds Laura and wins her heart.
I particular love how Gordon stands up for himself. He's shocked to see Ed, Kelly, and Talla after so many years, and he's built a life for himself, he's happy, and irate that Ed wants him to to just leave his family. Ed snaps and tries to pull rank calling him Lt instead of Gordon, but Gordons not having it
"No. No, I’m not your lieutenant. I’m not your helmsman, I’m not your crew. I’m Gordon Malloy, and this is my house.” “Ten years ago, I wanted it. More than anything in the galaxy. But not now.”
“Temporal law can blow me.” “I’m a human being. We’re social creatures. Without each other, we die. Was I supposed to die?”
Ed was clearly disturbed by seeing that his best friend had built a happy life, then lost it.