Deans love language
Dean might not be good with words or saying how he feels but Sam doesn't need him to speak to know how Dean feels. It's always been there in Deans own way of telling Sam, through his touch.
When Sam was little it was hugs when he was hurt and kisses on his head when he was scared. It was curling up together in their bed at night so that Sam didn't know where one of them ended and the other began. It was the way Dean scooped him up and spun him around when they were happy and also shielding Sam behind his back when their father was drunk and angry.
As they got older Deans love language changed to shoulder bumps to say I love you and a pat on the back or hand on the arm to say I'm here for you. It was the tight hug that said thank God you're alive because I need you so much. It was the brush of a knee under the table just to say you're not alone or the hip check to say you're a dork but I love you anyway.
It seemed only natural the first time Dean kissed Sam on the lips. It wasn't sexual or weird. Sam had been knocked out and when Dean ran to him and found him alive, he couldn't help but place a chaste kiss on Sam's lips when he woke up.
It wasn't something that happened all the time in the beginning but as time wore on and they became more comfortable with this new word between them it happened more often. They the kisses got deeper, sharing more feeling.
As the years wore on and they lost more people they clung together more and more at night. They had always comforted each other by touch, especially when one was scared. When Sam had nightmares, Dean always held him till he settled and fell back asleep. This became more difficult once they moved into the bunker and had their own rooms but if Dean noticed Sam looking too tired, he would turn up in Sam's room and slip into bed with his back pressed against Sam's to say I'm here you can sleep now.
If Dean was the one not sleeping or having some of his own recurring nightmares, he would leave his door open at night and Sam would slip into his bed and wind himself around his brother, showing him the same love Dean always gave to him.
It seemed only natural for the kissing to escalate, especially after loosing Mom, again. The grief bound them even tighter together, if that was possible, and in their need to comfort each other they found yet another way to say what they felt.
As the grief abetted enough to move past the sadness they found they really liked to give each other pleasure and even though neither had ever been attracted to a man before, what was happening between them was the best sex either of them had ever had. Probably because it wasn't just sex, it was telling each other how they felt without speaking. Sam started appreciating his brother's perfect features and his sexy legs, while Dean loved to touch Sam's wide chest and worships his big dick.
By the time Chuck was defeated and Eileen moved back to Ireland Dean had long since given up the shallow hookups that had defined his adult life and was happy to settle down into a domestic life with Sam who wanted that as well.
In public Dean stopped trying to hide his feelings for Sam and would lace his fingers through his brothers, holding his hand as they shopped for food or walked around town. He would just randomly place a kiss on Sam's lips, especially if someone was checking either of the boys out. A way to say they were taken and happy about it.
Sam loved this side of Dean and was happy that his brother was finally allowing himself the freedom to show his feelings more, and not just with Sam. He became a hugger with their friends and would throw an arm around Jody or Donna and give a squeeze just to say he cared.
It was their first Christmas after Chuck and they got a real tree with decorations and everything. On Christmas morning they sat under the tree, on a rug they'd placed in front, and opened their gifts to each other and, of course, the bone they wrapped for Miracle.
As they finished up Dean pulled out a wooden box that was hidden inside the tree and handed it to Sam.
It was small and polished with a latch on the front. When he opened it there were two identical rings inside. Both were gold and as Sam pulled one out he saw that an anti possession symbol and a devils trap were etched on the inside along with the words 'forever mine'. On the outside of the ring was a raised silver circle that Dean explained was pure silver so if they shook someone's hand it would burn if they were a monster. Sam smiled at this.
"I was wondering if you would, if you would be my life partner." Dean asked hesitantly, afraid of the answer.
Sam looked at the two rings feeling such love he couldn't speak so he placed a gentle kiss on Deans lips and slipped one of the rings onto his brother's shaking finger. Dean took the other ring from the box and slowly slipped it onto Sam's finger as he looked him in the eye.
"I love you Sam. Always." He said simply.
"I know Dean, you tell me all the time." Sam said, and at Deans confused expression Sam pulled him in for a deep kiss showing him his answer rather than telling him.