Now a girl has a crush on me.She secretly told one of our common friends that "I am committed but I have a huge crush on this guy(me)."She does not know that I know this.moreover she does not make me feel or show that she likes me.after getting to know this(that she has a crush on me) I have started thinking about her too much and feeling bit infatuated.What is the way out?

You're only thinking about her now because of this information you just learned. Realize that she is with someone and forget about her.

Forget about her. She is with someone.