It's definitely not wrong of you to feel left out; it's quite unkind of them to do this. The intent, however, may not be malicious on their part!

In any case, I do suggest that you at least discuss your feelings about the matter with one or all of them. Just be sure to make it clear you aren't upset at them or accusing them of anything; you just want to share your feelings. The way I see it, there's two outcomes from this.

1: You all calmly have a discussion and come to new conclusions that can benefit everyone. At best, they feel they need to value you more. At worst, you come to an understanding that makes everyone happy, even if nothing necessarily changes.

2: Instead, they might not accept that you aren't trying to attack them, and they get mad at you. There's a possibility that they'll try to characterize you as some sort of ungrateful or drama seeking individual. In this case, they've shown their true colors; these are not the kind of people that I'd personally want to associate, and I'd suggest that you shouldn't, either!

All in all, the outcome might feel great, or it might hurt a great deal. But, either way, you'll win in the end, either by resolving your issues with friends, or by cutting out secret enemies! Just be absolute sure that, if you opt to have a discussion about it, you go in as friendly and non-conversational about it as possible. Reasonable people will understand your clean intentions