you don't
Be honest with him and tell him how you feel, it's hard, i know but you will have to know babe
Ask him. If you can't talk to your boyfriend and expect an honest answer, it may be time to move on.
You should just ask them and be honest.
Find someone that is honest with you and you are honest with him.
be honest with your boyfriend
be honest sit him down and take away the remote and lay it on the line
Be Honest.
Dump him. If he can't be honest with his friends then he won't be honest with you.
Just be honest, if you have got a boyfriend then tell him you have, if you haven't got a boyfriend then tell you haven't got a boyfriend :)
You ask him. If he won't tell you, find another boyfriend. If he gives you anything other than a straight, honest answer, find another boyfriend. If you plan on spending time with him and maybe planning a life together, you have the right to know.
Be honest about the way you are feeling.
The most important thing to do is be honest. Be completely honest no matter how the outcome is.