Disclaimer: No I don't anything and never will. I hate these disclaimers.
Angels don't have opinions. They don't have brains. No willpower. No emotions. They run on blind faith for a man that only four of them have seen. Basically they are just mindless robots. This thought makes Gabriel mad.
Ever since he had abandoned his family in search of bigger and brighter things, Gabriel had watched the angels from afar. Every single order given was followed with enthusiasm of serving "God". HA! God! What a joke. The guy showed himself to four angels. FOUR. That is a pretty small number if you ask Gabriel, which no one did but he would say it was anyway.
Gabriel liked it better down on Earth. It had the finer things in life(aka chocolate, wine, and women). Leaving heaven wasn't hard for Gabriel at all, in fact, he revelled in it. Leaving meant freedom do what you want, when you want, but it also meant you could think for yourself. Which was a scary thought to anyone who only obeyed mindless orders since the day they were created.
However, the day that Gabriel met Sam was a whole lot like living in Heaven. He couldn't think straight, he felt as if he had no willpower(no matter how much he wanted to believe he did have some that day).
Ever since then, Gabriel had run on blind faith for that boy, and learning Sam's fate hadn't helped a bit. He hoped that Sam would keep making the right choices, he needed Sam to make the right choices, because Sam was one of those guys that wanted to make the world better without the Apocalypse.
Gabriel wouldn't say he had chosen a side, especially not in front of Dean, because if he told Dean that he was on Sam's side, Dean would go ballistic. And Sam would ignore him, and avoid him. And then Dean would get mad at Sam for choosing him, the Trickster. The one who had killed Dean over a hundred times. And Gabriel just couldn't deal with a broken Sam now.
Somehow he had to let Sam know that he was on their side, but he knew that Dean would pitch a hissy fit and tell Sam that he can't be trusted yadda yadda yadda. He wanted Sam to trust him because he was tired of being alone, of being the one everyone hated. All he wanted was to love Sam, and was that so bad?