Basically what it says on the tin - Bucky wants Steve to punish him for having sex with other people (i.e. being assaulted.)

Would definitely prefer if this skewed cathartic rather than self-destructive. Bucky knows it wasn't really cheating but is wrestling with feelings of guilt and shame and is turned on by the idea of Steve being angry at him/possessive. (Would also definitely prefer if Steve gets turned on by the fantasy too; even if he maybe has some trouble at first with the initial premise.)

Bonus points if the punishment focuses heavily on "reminding" Bucky who he really belongs to (Steve), how Steve's going to keep him captive so no one else will ever get to him; Additional bonus points for lots of slut shaming/victim blaming