[Gmac]

Tough call, I'm not sure we're getting the whole story here. If you didn't bang girl A and never set any ground rules with your wingman that's one thing. Always set boundaries. There is a level of transparency and mutual respect that is implied when you go out with other guys, but just because you "opened the set and chose girl A and he got girl B and it all went really well" doesn't mean jack shit if you two didn't discuss protocol. So I'd say it's on you to determine whether or not you forgive him, but in the future make sure you lay down the law ahead of time. You should always choose your wingmen wisely, but never assume just because you talked to a girl that she's yours, or that it's even implied.

Edit (because I missed this part originally): His response "that's none of your business" was based off of what? It does seem a bit out of line. Did he know you were still pursuing this chick?

I had a close friend who I found out was banging a ONS of mine for a few months (just on the outskirts of our social circle) after I explicitly forbade him. Did I have the right to tell him not to once I'd cast her aside? No. Did I lose respect for him after I found out? Absolutely. You have to pick and choose your battles. Sometimes you're better off forgiving and forgetting. At other times once a line has been crossed there is no going back. You need to decide where you stand.