Am I selfish or just a doormat

So, for those of you following the extremely boring relationship saga of my life, here's a synopsis:

-I broke up with my now ex girlfriend at the end of June. The proverbial straw that broke the camel's back was essentially "I can do whatever, you just have to always be there to support me."

-during the time I was shellshocked from this, my (male) cousin got engaged. Wedding invite was sent to my family, not me directly. I was signed on as going by my mother.

-more or less recover, still bitter and angry however. Reclaiming a lot of my time and energy.

-get certified as a Scuba diver over the summer.

And now we come the Crux of the issue. The last dive trip for the year is the same weekend as my cousin's wedding. Cousin and I haven't been close for years. (Polite nods and conversation at family gatherings is as close as we get nowadays, different life styles is all.) Express interest in going on dive trip to mother instead of going to wedding. Hear no response. Think. "Alright, everything is cool then."

Then I get a phone call from my aunt who never calls me. "WHY ARENT YOU COMING TO THE WEDDING AHSHAHNG!?!??!"

Now I'm blindsided, agree to talk to my parents about it. Mom had told aunt that I was going diving instead of wedding. Ask why, because this wedding wasn't catered or anything of a financial issue. Explain that I'm still angry and bitter about the breakup and really don't feel like celebrating love and joy with the new couple, as that would just make me feel like hot garbage. Get "well, she expects you to come."

What. The. Fuck. Mom. I could have just sent them a goddamn card with 100 bucks in it and all would have been fine. Literally no one on my cousin's family would have missed me except for my grandparents and you guys. Now I feel like I have to go or else I'll be forever cursed with the evil eye or story time about how much of a piece of shit I am because I didn't go to their hillbilly fucking wedding at every goddamn family event.

And you wondered why I got into such a terrible relationship.

So, should I stick to my plan and go diving or suck it up and go to the wedding?