I find that hard to imagine since he's been depicted as having a very loyal and dutiful personality. Also, definitely not a player. However, cheating would be bad, so I may condone a deserving "ball kick" : P
Thank you for accepting my choice to punish him. In the very, very, very minuscule chance that BW would make some mechanic where Cullen and some other character flirt even though Cullen's romance is flagged as active, I'd just bail and go for someone else.
I'd rather not physically harm him or his hypothetical partner in cheating, but since (as Narcia said) he's all Lawful and ****, and since at least in the games I've played Bioware has only had an LI cheat on the player once, I have no idea why this topic keeps coming up. :\
I don't know either! I was just reading a few pages back and saw that someone was still very preoccupied about the topic and I felt I needed to say my piece.