Gabriel fell head over heels for Sam Winchester. When he met him as a janitor he never expected to like him so much.

When he met them for the first time, he had simply noticed that Sam was hot. Really hot. But hey, he thought plenty of people were hot, so it wasn't a big deal that Luci's vessel was.

But it was at the mystery spot that he realized that he was totally and completely screwed. He'd been planning to let Dean stay in hell, but those eyes... Sam had the most adorable puppy dog eyes he'd seen in the millennia that he was on earth. And he just couldn't say no to that.

When he'd thrown them into the TV land thing, he'd known that he'd probably end with him telling them who he was. He didn't mind it. Part of him hoped it would make Sam a little bit less disgusted by him.
He didn't think it made a difference.

He died for Sam. He didn't expect the plan for him to stay alive to actually work. But he was totally prepared to die for Sam.

Because he'd fallen head over heels for Sam Winchester. And he could never tell him. He could never talk to him. He could never tell him that he was still alive, or else he'd tell him how he'd fallen for him.

He'd rather die than face the sort of rejection that that'd get him.