One shot!
Sam bet Dean that Dean can't have sex with Cas for a week. If Dean loses he has to do anything Sam says for a day and vise versa. Dean starts ignoring Cas more and Cas starts to wonder what's going on. He tries to make a move on Dean while laying on the couch on night and Dean pushes him away. Cas feels bad so goes to bed early that day. In the morning, Cas finds Dean and Sam talking. Dean tells Sam he can tell Cas might know. Sam said Dean should just tell Cas about "her" referring to the bet. Then Dean says he doesn't want to lose her though. Cas just gasps and leans against the wall. He feels tears breeching his eyes as he starts to cry. Dean walks into his room seeing Cas curled into a ball. Dean ran over and touched Cas "Baby are you ok?"
Cas just pushed Dean away. Dean walked out into the living room and Cas comes out about ten minutes later. "No Dean I'm not ok!" Dean and Sam share a glance before Dean nods.
"Tell me what's wrong."
"You are cheating on me!" Dean's eyes widen and he leans back.
"Cas, no I'm not."
"Yeah you are! I know all about her! And how you don't want to lose her!" Dean just walks up to Cas.
"Her is a bet." Cas just tilts his head in confusion. Dean looks at Sam. "You win Sam. I'd rather lose this bet than lose Cas." After some explaining Cas forgave Dean and Sam. The next day Dean had a lot of shit to do.