Sometimes these things happen.
I have been friends with a group of women since we were children. Within that group some are closer to each other than others so there will many times when just 2, 3 or 4 might do something together (from a holiday to a night out). That is never an issue. But it is quite a definite group of about 8. We've all been to each other's weddings, etc.....mostly.
One of the women got married a few years ago. I was invited to her hen do (by the bride - she gave a lost of names to the person organising it), was around for quite a few discussions about the wedding plans, etc. But I wasn't invited to the wedding at all. Initially I wondered if there'd been a mistake so I asked one of our mutual friends. It wasn't a mistake, my invitation hadn't got lost. I wasn't invited. I was a little put out as we'd all been friends for a couple of decades and, as I said were a definite group. But the bride and I weren't as close as she was to some of the others (if either of us needed a shoulder to cry on, we probably wouldn't have chosen the other on to turn to initially, for example).
I didn't dwell on it. I accepted it the right of the bridge and groom to invite, or not invite, whoever they wanted. Yes, I was a little hurt but as the bride was still being perfectly friendly and nice to me I decided there wasn't any deep meaning behind the decision. When I got married, about a year later, I was maybe slightly petty and didn't invite her either. But other than that our friendship has carried on as normal. A few years later we are still friends, still part of the same group and no closer but no less close than we were before.
It's natural to be upset over this but perhaps don't let it get to you too much? You could check with another friend from the group (not your insensitive 'best' friend) that there's not been a mistake. If there hasn't, you can dwell on it and let it affect the dynamic of your friendship with the bride and the rest of the group or you can just chalk it up to experience, accept the fact a bride gets to do whatever she wants (within reason) on her big day and enjoy what the friendship group brings you in the future.