Well first of all, you probably should have kept your mouth (but your probably a young buck and impulsive am i right guys?). But the deed is done. The choice is yours at this point.
Do you love your lady? Or is it worth it to tell your buddy that he needs to find another bud to go with him? Do you value your friendship that much that you can tell your lady to hit the road (for a couple of hours)?
You have three choices here;
Sleep with your lady
Sleep with you buddy
Or get some Aveeno and get intense with your fist.
Just tell the damned truth to everybody and save yourself some grief.