Betrayal?

I have been considering for a few days now.

Apparently, I am flirting with a girl that my friend likes so much.
So, it makes me feel like I am betraying him.
However, the girl shows no interest towards him.
Yet, he still does not give up.

In one hand, I felt like I had done something I should not.
But, in another hand, its not my fault. We are just fighting fair.

Nevertheless, I am afraid that my friend would know about this sooner or later.