Isn’t the OP the bull? It’s the OP’s wife’s ex who is the cuck. I’m not agreeing with the asshole but I think the definitions are mixed up.

What you do now is let it go. Don’t hold onto the resentment because at the end of the day, they didn’t care enough to spend time with you. Some may have had good reasons. Others may not have.

It’s their issue. The best you can do is to spend more time with the folks that did come. Ask the 5 friends (or one or two) if they want to do something with you next week. Pick an activity. Doesn’t matter what.

A lot of commenters here are saying a lot of similar things. I’ll offer my own insights.

As people get older, you have less time. Between maintaining a relationship, doing chores, work, etc, there are so many hours to do things.

As a result, a lot of FOMO happens. It’s not about you. It’s them. They may plan to come to your birthday. They may even want to. But suddenly, something else comes along that they want to do instead.

I don’t plan big events anymore. I’m in my 40s and just dgaf whether people make time for me or not. I’ll ask one or two friends if they’d like to go out to dinner for my birthday or some event.