Should you be concerned? Well the answer is no.........are you concerned? I take it the answer is slightly. The good news is your feelings are natural and normal. The bad news is if this is a annual thing it is unlikely he is going to want to change it regardless of how you feel. And that leaves us with a far bigger and more important question.
Can you accept this and be ok with it? The fact is if things get serious in your relationship and you marry is this going to cause conflict in the future. The fact is many friends feel more comfortable without the new spouses when doing reunions, one reason is many new spouses simply do not get along with the old friends and then everyone gets tense and often the friendships simply fizzle out. For this reason it sounds like the group has made a choice that everyone agrees with.
It is unlikely there is anything really to be concerned about, since all the spouses are not invited it isn't like it is just your boyfriend does not want you there. At this point since you are just boyfriend and girlfriend there really isn't much ground for fighting this. Though if it will cause a issue in the future it may be something you will want to talk with him about when he comes back. Let him know how it makes you feel to be excluded from him and his friends. Let him know that you understand why the decision was made but if you are going to share everything in life in the future then this is something that will need to be addressed before it becomes a conflict between you both.
Wow. I really needed to hear that. I needed someone to validate my feelings, especially since my b/f does not understand me feeling weird about it. I mean, they go to a resort, drink & eat heartily...things can happen in those situations if boundaries are not clear! Though, in my heart I do not have any reason to distrust him. He DID, in fact, say that the arrangement will likely not change unless the whole group agrees.
Also, I'm kind of jealous of that kind of group friendship. It's not something I have but I am glad he does. I don't want to be selfish or act insecurely or deprive him of something that is such a blessing to him.
I understand this is frustrating to you, it is good that you do not want to take this from him. But do not be to hard on yourself for feeling weird about it either. Most anyone would feel a little weary knowing their husband was off with friends drinking and eating and spending the weekend together.
The reality is though that this is where trust comes in........while it may take a while for you to get over the feelings you are having you must learn to trust him on this. If you can not trust him you will struggle with this for a while. In the future things may very well change, he may change his mind about this or the group may eventually decide that this is not working and change the rules. The key is try to be patient and trust him.
You may also want to consider making this a special weekend for you as well each year. Maybe with your mother, family or a friend take a weekend trip to a spa or hotel and enjoy yourself. The fact is if you are looking forward to you time.......then his time will not bother you as much.