Re: So confused! Am i doing the right thing? Please help me!
Don't waste any more time waiting for the first girl. You'll never be able to lead a real life if you turn away every relationship thinking, "But what if....?" especially when there's such little chance that anything will come of it. She knows how you feel and has chosen to invest her emotions in another, so I think we can safely say she doesn't feel the same way about you. As hard as it is, you need to move on from her.
Don't ever date someone out of pity- it would be much more cruel than rejecting her. You don't like her like that so don't try to force the relationship. It would end badly for both of you and very likely create such awkwardness that you wouldn't even be able to remain friends. Been there, done that.
It's just common sense. You feel some attraction for the third girl, she feels some for you, you have next to no chance with the first girl and you don't like the second girl. "Door number 3, please, Bob."