Wishing you were dead over a girl who, im going to be honest, has had little or no interest in you by the sounds of things is a little bit extreme.
If its taking a toll on you this badly, cut her out of your life. She is making you feel like ****, so there is little to no point in even trying if:
1. She is kissing another guy
2. She hasnt shown any interest in you other than 'smiling'
Move on, find someone else. Time heals all wounds.