Friend Trouble, he's ditched us.?

We're 15 and one of my best guy friends has been going out with this girl for about 4 months now. To begin with we were really supportive of him but now its just starting to get annoying. He walks her too school, hangs around with her before school starts, stays with her all lunch, walks her home, goes out with her in the evenings and also the weekends. He has absolutely no time for us anymore. The only time he does hang around with us is in lessons, (she is in the year below) and when she isn't available. He just thinks that he can waltz in back to us whenever he feels like it. We are his second best and he ditches us the moment he gets the better offer. Our group of friends really like him, but we want him to realize that he just can't keep taking us for granted anymore. What can we do to make him realize!? Because now they're both becoming borderline obsessive over each other!