The same as above too. The girl in the club: it sounds like you were thinking too much; it was worth a shot.

At the party: you missed a chance of getting laid, but it was the right thing to do. There will be plenty more and your conscience/karma is clean.

Your friend's sister: go for it. I did; it was great. He was a bit mad at first but then he was really happy as he saw that we just really liked each other. We are still best friends.