If it was me, I'd quietly withdraw from the group. I wouldn't make a scene of trying to find out the what's, wherefores, and why's of the situation. You're unlikely to get an honest answer anyway as most people tend to cover their backs and give cop out answers when called out for shitty behaviour.
The biggest tell in this situation is that you asked what their weekend plans were and none of them said anything. Any chance that it was an oversight to not invite you died on that spot. It was intentional.
I personally couldn't remain in a friendship group that would deliberately exclude one person from it without explanation. For me, it would be more awkward to hang around where I've clearly been shown I'm not wanted than it is to just quietly bow out.
I've had similar happen and whilst it didn't result in the end of a friendship because it wasn't anywhere near as cut and dry and bad as this-it still stung so I imagine this hurts even more. One of my closest friends would always go on nights out with her friends, people I'd met and got along with-and then afterwards say, "Oh, you should have been there!"
After not inviting me or telling me about it so I could have been there. It was hurtful because whilst we had separate friendship groups, I always made an effort to include her with my other groups too-so it would have been nice to have had that reciprocated rather than finding out after the fact and being told that I should have went.
That one was a genuine oversight (multiple oversights) but this seems like it was deliberate and intentional. I'd not continue a friendship like that. I don't have time for people like that.