Walk away spouse- what else can I do?

[a girl]

Be really careful not to use the kids in any way during this, even a passive-aggressive one. I know "I wasn't invited" seems harmless, but I promise you, it causes them anxiety.

When my S7 asked if I could come to Ikea with him and daddy, I just said, "Oh, sweetie, that's a you and daddy trip!" Obviously your son isn't at the age for that, but you have to find a way to answer his questions without making him feel put in the middle or causing your W to *think* that's what you're doing.