Dean Winchester had no idea when exactly he had fallen in love with Cas. There was no one single moment that he could point to if someone asked him "when did you know?" Dean knew some people didn't see him as a very intelligent man, and he was fine with that, but he had spent so many nights trying to figure out how it happened. The best he could figure is that it was happening all along, in all the moments they spent together, in the corners of Castiel's honest smile, in the office at work, growing like an ivy slow and stealthily, only realizing he was in love with the man when he was already neck deep with no escape.
Dean had fallen in love with Cas, he knew that and felt no shame about it. The only problem being that Dean Winchester is no homo. Now, as far as Dean was concerned there is nothing wrong with being a homo, he just wasn't one of them. Dean wasn't attracted to men, he was attracted to just one man. Maybe Dean had always been a little gay, whatever. The more he thought about the situation, the more he realized that none of it fucking mattered.
Castiel Novak was the first person Dean could ever say he's loved. .He tried to love Lisa, he really did. He didn't want to marry her, but he felt that it was only right considering he knocked her up. They had only known each other for four months. Dean can't remember why he begged Lisa to marry him, it all seemed so irrelevant after she miscarried. He couldn't just divorce her then, so they trudged through an unhappy marriage for years. When Dean had resolved himself to the feelings he had for Cas he knew that it was time to let it go; Lisa had thanked him and flew home to her family in Vermont.
Here he was, spending Christmas with the man he loved, and a boy that was quickly winning his heart. Dean didn't really have a plan, he just wanted to spend as much time as he could with Cas and Ishmael, to have them close. If Dean had it his way he would slip into Castiel's life the same way that he had fallen in love; Cas wouldn't know until Dean was so much a part of his life that Cas would never give him up.
Dean wished that he was better at being gay. He wanted to reach out and tell Cas how he felt, but he couldn't. If Cas could love him, if he could say it first Dean could scream it from the rooftops. If. What if he told Castiel, what if he opened that door only to find rejection waiting for him behind it? Dean would break his own heart every day and be nothing more than his friend than damn himself to live without Castiel in his life.