Well, one reason is that if he always talks about her or gazes at her or always wants to look his best around her. He will probable try multiple times to try to get her attention and is trying to impress her. Or he could be a bit shy around her. He would sometimes try to flirt with that girl. (Most common way is always complementing her). Either way these are a few signs to signify that he might be crushing or hitting on her. I really hopes this helps you!
you will know that he likes your friend because he will always bring her up and he will want to be around her.
They will eventually tell you
don't
Your friend tells you.
Be honest, and ask him.
ask him
how he lookes at you
Woman's intuition. Actually, talk to the guy or have your friend guy talk to him for you.
Tell her the truth.
She likes you and that other guy and her boyfriend but does not know who she likes best.
You wont know until other rumors, if your friends knows that a guy likes you, and if they talk, your friend and the guy, that means the guy wants it to keep it a secret and told your friend to keep it as a secret, if he/she does that means he/she is a good friend to the guy, so wait until the guy asks you out, theres nothing for you to worry about
If your guy friend likes you tell him how you feel about it. If you like him let him know. If you don't, break it to him easily but not to easy that way he understands and you still have a friendship.