Admittedly it was a time period where we had been traveling with the in-laws for several years but not every trip was with them----
A few years ago we decided after my husband got back from his field assignment that he had basically been away from home (coming back home every two weeks) for 13 1/2 months to go to Hawaii as kinda a way to celebrate and relax.
At dinner one night eating with the in-laws they had asked me what we would be doing when my husband got home (my husband wasn't there at the dinner) for good and I replied that we were planning a trip to Hawaii. My mother-in-law immediately started talking about how fun it will be and how she'll have to look at flights and what to do....and I sat there kinda stunned. Nothing I said had denoted it was a trip we would all be taking. She had indeed asked me what my husband and I would be doing when he got home. Also admittedly she's the type of person that does kinda invite herself along for things at times.
I did as gently as I could let her down by saying "oh this is a trip we are going to take on our own actually". I softened the blow by saying we could look into doing something else with them for a later date (which we did). No way was that trip going to be a family trip. It was going to be a relaxing spousal trip

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