I'm trying to find a fic that I read a while back, but have been unsuccessful in locating. The main pairing is Steve/Tony, but it begins with Tony/Pepper in an open relationship. Steve and Tony end up fighting after the team deals with a villain. Steve shows up in Tony's workshop as Tony is removing his suit (?) and starts yelling at him for not listening to orders I think. The argument turns into heated sex when Tony kisses Steve as a means of shocking him (I think it had to do with Tony saying something like "Yeah, well, I bet you wouldn't expect this!" though I could be wrong.) This keeps on happening during arguments between them and the more they do it the more their feelings for each other begin to change. Tony and Pepper's open relationship has a rule that is something like not sleeping with anyone twice or no feelings for the people they are sleeping with... I can't remember, but eventually Pepper I think breaks up with Tony when she realizes Steve and Tony are in love with each other. It ends with Steve and Tony officially getting together.
Thanks to anyone who can point me in the right direction of this story!