Most Helpful Guy
Lol welcome to the friends zone, many guys can relate here. I read further down you said no, which is good but never tell a girl you don't believe her. What does it matter anyhow, she doesn't want to date?
Next time use the line "Okay, when it doesn't work out with him let me know" or "he can keep you busy when you're not with me." Avoid calling women out on their lies here because it won't change the situation, you're zoned to friends.
I applaud you on not falling for the friend trap, most likely you would have to initiate "friend dates", pay, and be her emotional tampon. Move to the next