Here it is: don't confront girl #1 like you would a clockblocking dude. That won't end well (Hell hath no fury and such). Instead, just be honest with girl #2. "I really liked spending time with you and I'd love to see you again. Can we get together Saturday?" If she shoots you down, then politely ask for an explanation and maybe even specifically ask if it's because of girl #1. If it is (and if it looks like there's no chance of redemption with girl #2,) THEN go to girl #1 and say "********* me again and I'll c%#tpunch you so hard your grandchildren will have miscarriages." *mic drop*