What are ya thinkin?!

Alright, I ran into a little dillemma followin my senior prom, And I need some advice on how to deal with all people involved. OKay I took this young Lady I was sorta feelin to our 12th grade prom, well we had planned the entire nite out, well after all of the ceremonies, we begin dancing, I'd say about an hour into the dance the two of us begin kissing and laughing havin fun in general. The kissing continued until we decided to go to a more private place (the car) and kiss in private. Well eventually, I took her home said goodbye kissed her on the cheek. She called me the next day and we talked for a while about the previous nite and how much we had enjoyed ALL of the festivities, ya mean. Well on Monday i got to school and she was sort of stand offish, but that can be expected with someone of her limited "expierience". But around of the end of the day i see her walking and holding hands with some junior in the hallway. And now there in a relationship. But my question is to the ladies if we were feeling each other so much on saturday,and she was/is feelin me whats going on wit her? And how do i approach this situation while also being a gentleman? But to the fellas should i hold a grudge on this girl, what about this dude? Just send me some feedback.