Point one: You are upset at not being invited to your cousin's wedding.
Where other cousins invited, and it was just you left out?
The fact that nobody asked after you does not seem to favour this version. They probably did not expect to see you there.
But whichever it is, in the end it was their wedding, and it is their choice who they want to have with them on their special day.
Point two: You did not see your aunt before she died.
Blaming this on not being invited to the wedding seems -sorry - pretty lame.
Point three: You decided not to go to the gathering after your aunt's funeral. Seems like a 'you did not want me then, now I don't want to either'-reaction.
That is your decision, why it would puzzle other members of your family I can understand.
Point four: What all this now has to do with your aunt's birthday I have no idea.
If you don't feel like seeing your family, don't!
It is not such a big deal.
I hardly ever see any of my aunts and cousins.
We are not that close, either!