Buck needs regular sexual contact to survive, and if he's not getting it in real life, he gets it in dreams (with less control). Take that wherever you want!
A few ideas, though.
He tries really hard not to go in Eddie's dreams, but nobody else tastes as sweet.
Dream Eddie is kind of sadistic and kinky and fucked up about sex, but when they finally get together RL Eddie is super gentle and vanilla. Buck guiltily keeps fucking dream Eddie as well and tries not to feel like he's cheating.
Incubus!Buck (Incubuck?)
A few ideas, though.
He tries really hard not to go in Eddie's dreams, but nobody else tastes as sweet.
Dream Eddie is kind of sadistic and kinky and fucked up about sex, but when they finally get together RL Eddie is super gentle and vanilla. Buck guiltily keeps fucking dream Eddie as well and tries not to feel like he's cheating.