Mmmmm, that's gorgeous. I love how all the emotions and the physical sensations just slip-slide together here:

He let his fingers slide back and his cock slide in, and Justin pulled him in with his legs and arms, with his voice soft and rough, saying something that sounded like "I love you, I want you" but was only his name.

*melts*

Brian's teeth bit into his own lips, and he turned his hand a little to the right, seeing Justin relax and let him in. Something in the way his knuckles worked their way inside, Justin's hole stretching around them, made him crazy, made him want to bite Justin, slap his ass, pull his hair, press his fingers into his hip so hard he left marks.

But the hand half-inside Justin was gentle, gentle

Probably my favorite part. The repetition of that word is perfect.