It's taken years for this to come to pass. Five, to be precise. Castiel never told anyone after Gabriel appeared in his Metatron-induced daydream. Well, not on purpose. He had mumbled the name once in his sleep, Sam sitting not five feet away from him. After that there was extensive questioning until it eventually lead up to Sam summoning the archangel with an old Enochian spell.
Dean was taken aback, Castiel was accepting and happy, and Sam - he was something far more than ecstatic. Gabriel took it as more than an invitation and his flirting soon became shameless and lewd, but still Sam would just blush whenever Gabriel tried to make a move on him, making some excuse and leaving with a hard on and a red face. But Loki wasn't always set on getting in Sam's pants; sometimes he would just slink in, catlike, on silent feet as the hunter was doing his research and just curl into his side quietly. He would make Sam the energy/protein shakes he seemed to love so much; even left lollipops in the shape of roses on the hunter's pillow. Despite what his Trickster side has to say, Gabriel really is just a big cuddler and hopeless romantic.
Still it took months before their first kiss and even longer before Sam would even allow his new boyfriend to see him without clothing. Eventually it got to dry humping then to the occasional blowjob before finally ending up here:
Gabriel is more than happy with this situation, Sam's thick member buried deep inside him as the archangel's fingers bury themselves deep in his lover's silky hair, his back pressed against the wall with Sam's strong hands on his waist to hold him up. It's slow and hard, but he doesn't want it any other way. He wants it to last. This bond between them is something he's never felt before - not even with Kali - and it's strange, somehow making every kiss more meaningful, every little touch electric, every look magical. And don't even get Gabriel started on how the cock inside him feels.
There's a warm heat in his stomach, not just from the building orgasm but from the bond he and Sam share, the pure love in every movement of them, pushing against each other, panting and moaning in the other's ear. Fucking perfect, Gabriel nods to himself.
"O-oh, Sam…" He breathes out when his prostate is hit - even that being more sensitive somehow.
Sam kisses his lover gently, his hips rocking slowly into Gabriel but ever-so-wonderfully. "Have you ever felt this way?" he breathes out against his lover's mouth, Loki grinning a little when he realizes this breathtaking feeling is far from one-sided.
"Never." Gabriel whispers and soon they're both coming with soft cries of their lover's names.