Gabriel resented his father for a lot of things. For being absent for so long, for never interfering, for letting Michael and Lucifer continue to destroy everything. But what he resented his father for the most was what he'd done to Sam.
Sam, his big lovable moose who was damaged beyond repair. Of course everything in his life had been set way before he was born. He was always going to lose his mother when he was just 6 months old. He was always going to grow up on the road with a barely present father and an older brother doing everything he could to protect him. He was always going to have to grow up way too fast. He was always going to be the one to free Lucifer, and he was always destined to be Lucifer's vessel.
The thing is, Gabriel hadn't cared. He was just another human, admittedly a pretty important one, but what should it matter to him? He had run away from his family, from all the fighting and drama a long time ago. So, how could he get dragged back in so quickly?
After Gabriel stuck the Winchesters in TV land, he started rethinking everything. He wouldn't admit it, but what Dean said had really hit him hard. So, he went to the boys and started helping them out. All he told them was he got bored and needed something to do. They were obviously sceptical, but eventually started trusting him. Then, at some point, he just started spending all his time with the boys. Travelling in the impala, hanging around their motel rooms, helping them with their hunts as well as the apocalypse.
They would never know, but it was all for Sam. He had fallen for the clumsy, giant of a man. It was all the little things about him. The way he would spend hours writing after Dean fell asleep so he wouldn't make fun of him. How the only time he looked peaceful in his sleep was when he was sleeping in the passenger seat of the impala with Dean singing along to the radio. The way Sam truly cared about everything, including him.
He didn't really understand how Sam could still do that. Still be so nice and caring after everything. There was so much emotional damage that couldn't be reversed. But Sam never took it out on anybody else. It was always just himself. The things Gabriel had seen inside Sam's mind made him cringe. He had never seen anybody so broken.
That's what he resented his father for the most. For breaking such a beautiful human being.
