To invite or to shun?

I talked to the ex about Ryan's birthday.
It's coming up soon and I wanted us to get our plans in order.

We used to take him somewhere, but now that he's married, he is uncomfortable with that.
So last year, we just had a little party at the house.  Grandma, Soon-to-be Step-mom, dad and me were all there.
It was nothing big, but we were all together.

I think Ryan really liked that.

But this year, the dad and step-mom are taking him to LazerTag.  With a friend and the friends' parents.
And then Sunday they are having cake with the grandma and the step-mom's parents.

There was never a thought to invite me.

So why do I feel obligated to invite them to stop over at my house for cake and ice-cream on Ryan's actual birthday (it's already my night with him)?

When I asked Shane if I could stop up to celebrate with them, I got the "I don't think her parents would be comfortable with that."

ARE YOU FUCKING KIDDING ME???

So Ryan is forced to spend the rest of his birthdays and special events splitting them between his parents?
This is NOT what we agreed to when we split.
We agreed that we would put our bullshit aside so that Ryan would suffer as little as possible.

And even if I thought his bullshit excuse was true, I don't care.
Anyone who has an issue with the fact that Shane comes with a twisted package can fuck off.
To be honest, the same goes for me.

I'm still trying to decide what to do.
For now I have to figure out what I'm buying my lil man for his big 9!