ooc: Castiel!Mun said I was allowed to be ridiculous. =)
She sat down beside him on the porch swing, reaching over to hold his hand in hers. He made no effort to move away and she leaned over, giving him a careful kiss on the cheek. Castiel imagined she knew how this went by now; what Brooke expected when it came to their guardian. He let her get away with just enough to make her feel wanted, but not enough to let her pretend that he wanted her. It had been made clear to her, many times, that his mission here was to honor a promise.
At first, she hadn't wanted him around at all. She didn't care that Dean had asked this of him, she could do it on her own. She was on her own, and no fallen angel with a frog in his throat was going to convince her otherwise. Dean and Sam were dead, and Heaven had called it a victory when they lost their lives averting the apocalypse. If you asked her, Heaven could go to Hell.
Her initial reason for letting him check up on them was that Matthew liked him. He thought Mr. Castiel was one of the good guys. They tossed around a football in the front yard or played cars in the living room, always where Brooke could see them. She was grateful when he kept coming back because he was one of the few people who could really get Matthew talking. Or rather, explaining. He taught Castiel about sports, video games, girls, and pie.
Eventually "Mr. Castiel" became "Castiel" and then "Uncle Castiel". It was three years after his fall when Brooke realized he was around almost every day. She spent another year debating whether or not she cared when he didn't show up, and ultimately decided that she worried too much for him to change his routine.
Every night, it was exactly the same. He showed up in time for dinner, always asked if he was imposing before accepting Brooke's invitation, and stayed until it was time for Matthew to go to sleep. As his bedtime got later, Castiel learned to stay longer. Cars on the floor became board games. (Castiel was always the banker. Matthew thought it was funny.) Elementary school homework became hard enough to baffle both Brooke and the angel who should have had knowledge of everything.
He put his arm around her when they sat together and watched Matthew make angels in the show with Jamie.
She couldn't imagine the guilt involved in being the survivor who ended up stepping into someone else's life, but Brooke didn't let herself go there. She was eternally angry; with fate, with life, sometimes with Dean for leaving her and Castiel for sticking around. And she understood, more than anyone probably gave her credit for, how horrible it was that she couldn't imagine their lives without Castiel.
Every touch, every kiss, and every kind word she offered still belonged to Dean. He was never far from their thoughts. But when she curled her body against Castiel's and drifted off to sleep, he was the one who carried her to bed. He took off her shoes, and he kissed her forehead. He got Matthew to school in the morning because she had been working too hard for the past couple of days. He took care of them, and fulfilled his promise.
Brooke would always wonder whether it was because he felt he owed it to Dean, or because Castiel genuinely grown to love them the way that they loved him. She'd never ask. The fact of the matter was, she didn't need the truth. She needed him.
It didn't matter what his reason for staying around was, as long as he stayed. Life had taught her not to be that picky.