What would be your intentions to NOT invite your W?
What would your W think, if you invited her? IOW, what do you suspect her thoughts might be about YOUR intentions?
So really, in the end... is it really important to invite her to go with you to get a pumpkin? If she wants to get a pumpkin for her place, she can get it herself...
You create your own memories for you and your son...
My W is getting a lot of feedback about my kids having a great time when they're with me... she mentions it to me quite a bit... she's "noticing"... but that does not mean she's telling me she wants to join in... until she does that... *shrug*
