I'm sorry for your trouble and sorry for our kids, who sometimes become pawns or spiders in the webs weaved by the adults around them.
Family is a tricky business after an A, indeed. I and DD are dealing with it, too. And for 5 years have dealt with it with my divorced parents. That's frustrating because my mother didn't cheat but walked off and often challenges my father to be at occassions or events where she is.
She wishes to stroll memory lane with him and some other things and it makes me gag.
I can't help but wonder if this is something of a challenge from you inlaw to you, but I don't know.
The post that speaks of First Communion being a religious event is a good one and relevant, though so are the others. An A is not a religious thing so inviting the people or person (OW) doesn't make sense, except for the inlaw trying to please your WH as a relative. Anyway..
It appears that you have some decisions to make, some similar to what I do. Weights and measures have to come out and my thought is that it is about your son, really and what's best for him.
Another thought is, what are you able to live with later and what do you want for memories, for both of you?
It wasn't decent of them to invite OP, that I agree with, or at best they should have approached you about it during the planning. For me, I would not have trust for them now.
It sure is a lot to think about and is awful that they made such problems for what is supposed to be a really nice and positive occassion.
Your son and the other boy worked really hard to arrive at this stage of their lives, for it's so much work to acheive your first communion, no matter what form of religion.
And it's not easy for you I imagine, because if you are not well inside, how can you be the best for him and provide needs for each of you?
The post that talked about going for the main events of the party is a good one and you would have that for remembrance for he and you later on. That has carried me through many dark times, when I've come through an impossible-feeling task.
This weekend, for instance, I went to my first occassion with the inlaws, without Perv there but with DD, and I did it. For once their rug sweeping worked in my favor and I only started to cry, but held it.
Maybe going for the cake, or if he gets a present if they are the type that plan the activities of these events, it may be good for your strength later on-but I can certainly understand if you had your own party and just let your son attend.
Sorry to write such a long letter.