Your boyfriend may be doing you a big favor by showing you what his priorities are. I agree that there could be a much more mature way to handle this. You don't say how long you have been together, but I suggest you take a stand now. If he really thinks he has to desert you to help his friend (there's no way you can do it as a couple?) perhaps he's not ready for a marital commitment. Offer to negotiate this problem with him (see my book, How To Be a Couple and Still Be Free) and figure out some solutions that will satisfy both your needs. If he won't work with you, he's telling you what your future relationship will be like, and you should pay close attention. Try cancelling a few dates with him because one of your friends needs you, and see what he thinks about that. That way, you'll find out if he's got a double standard or not. If he doesn't like it, you can point out it's what he did to you. If he doesn't mind, then it's his definition of how significant your commitments to each other are.
Either you're not is important as his friends, or he's not ready for a mature, adult partnership. A healthy relationship requires teamwork, and you need to begin building a team now, if you really want this romance to work. Make a strong attempt to work this out with him, but if he won't budge, then the writing is on the wall, and this relationship will not go much further. Read "Couples Can Cooperate for Success" for more help with this.