How should I deal with not being invited to a wedding?

Two of my very best friends are getting married next month and it seems that I haven’t been invited to the wedding. I’ve known the couple for a few years and have considered myself very close to the both of them. It’s not a small wedding. Everyone I know is invited. Both the bride and the groom have kept their distance for a few months now, and I thought it was just because we were all very busy, but now I can see that they were keeping distance so as not to have to have the conversation with me.
I’m always a sober and respectful guest and there hasn’t been any incident that would put me on the outs with either of them.
My gut reaction is to confront one of them, but I want to be respectful. I know they must have so much on their minds right now and I don’t want it to seem that I’m making this about me, but I’m really hurt. It’s sad to think I was wrong about how close we were.
Would it be too strange to just send a gift anyway? Or would that seem passive-aggressive?