Watch for little signs, like his wanting to be near you, or how he talks to you. If he appears nervous around you, its almost a sure bet he's into you. If he's trying to hang out with you more than you're trying to hang out with him, odds are he's interested. All boys are interested in you. That's how you should live.
Ask him.
make out with him in the boys bathroom
Message him after a few hours of your first day. If he replies quickly, you know that he is interested. But if doesn't, maybe he has changed his mind.
if he doesn't call you. or avoids you. he is cheating on you.
You don't - if it is a boy your interested in and it feels right at the time then do so but take your time to get to know him first instead of just jumping into something.
They really would like to know, what you are doing and who you are with. He is interested and wants to know what you like to do.
You've told him already, so he's thinking. It's really up to him now. If he thinks he's interested, or he is bisexual, then he will let you know. If he says nothing, then he's not interested.
Because your boyfriend is actually interested in you and the boy bands probably don't even know you.
He is interested in getting to know you.
Move on.
You just let him know that you think he's cute if your interested.
Be honest with everyone. Let the other boys know that you aren't interested, and let the boy you like know you are interested. Be prepared of him to choose his friends over you if he doesn't return the sentiment.