In this situation, OP's partner is being gifted a trip to Japan by his adult son, and the partner invites his adult daughter. OP is asked last because they haven't joined the partner on the last three family trips to Mexico, assuming OP might not want to go.
However, OP is dealing with challenging circumstances, including the recent loss of a main source of income, health issues, and the passing of their mother. Despite the stressful situation, OP wants to go on the Japan trip.
OP's partner is currently unemployed, and the trip will be expensive, adding financial strain. OP is contemplating using savings and business funds, and they'll also be subsidizing the partner's adult daughter, who doesn't have the financial means to go.
So what happens next?