What can I do?

I am no expert at this sort of thing, but I think you should tell him how you feel. You never know, he might be going out with this girl to make you jealous. You never know what could be there untill you have done something about it. So what you need to do is tell him, he might even feel the same way about you.

Let him know how you feel, it's not going to be as bad as you think it will. I know some people say that you shouldn't tell a friend how you feel, but at the same time I told a good friend of mine a few months ago that I did feel more than friendship for them. They didn't feel the same for me, but I let them know that even if we could never be more than friends I still needed them in my life, and we are still friends.

However, it does hurt like crazy to tell someone you love them and get nothing back, but at the same time it allows you to at least try (I say try because although it would be nice if you could just forget someone and move on you still think about them all the time) to meet someone else, and although I cry every once in a while anything was worth the chance to be with her, no matter how small the percentages and how great the pain.

I would wait until you feel the same (where you would do almost anything to be with them) before saying anything. If there is a chance that it could be a crush give it time and make sure that you do love him before saying anything, you don't want to ruin a friendship over a crush.

You know....I really don't think telling him at this time is a very good idea. And I tell you this with honesty from the bottom of my heart because I fell for my best male friend and told me all about how I felt about him when he was with a girl. We still remained pretty close, but it got messy, and I never ended up with him. I would suggest waiting until he's single. You can tell him, but don't set your hopes too high hoping he'll leave her for you. If you want to be safe and remain friends, I suggest waiting, but whatever you choose it is YOUR choice and whatever you feel is best and only you can know that, so good luck!