Also, this is a "Grown-Up" relationship.
Most Helpful Guy
I don't know why everybody is ganging up on you - you said you guys didn't make any plans, so how could you "ditch her?" - There were no plans set in stone, and from the sounds of it, it sounds like you made the right decision hanging out with a good friend instead of going out with some emotional flake...
You're under no obligation to make it up to her. It's not like you said "I'll meet you here" or anything like that and didn't show up... It wasn't like you when out with her and left her at some bar... there was nothing planned, so you don't owe her anything.
This is obvious people!