My husband and I hosted a big birthday party for his mother last month. We agreed to split the costs and responsibilities with his brother and his brother’s wife. We still haven’t discussed how much was spent and who owes what. My husband is going to meet with his brother next week to discuss it, but knowing him he will probably not include everything that we paid for and we will end up paying more than them. We are well-off financially and are both very generous people. We happily pay for everyone and everything most of the time. But because my brother-in-law is so full of himself and has a history of going around and bragging about how “affluent” he is, I don’t want him to get away with paying less than he owes.
Model #1:
C- The money hasn’t been settled for the birthday party.
T- Husband isn’t going to be honest with his brother about how much we actually spent.
F- Angry
A- Bug him about it and try to convince him that they should pay what they owe
R- Friction between my husband and me.

New Model:
C- The money hasn’t been settled for the birthday party.
T- I told my husband the total amount that we spent. The rest is between him and his brother.
F- Light and free
A- Carry on with my amazing life!
R- No friction between my husband and me.
My question is- Am I being foolish to trust him to do the right thing with his brother in the new model?