Dear Prudence is Slate’s advice column. Submit questions here .

Dear Prudence,

My boyfriend and I are doing a trial run before we get married. I am renting out my condo and we are renting a house. He has a 10-year-old son with 50-50 custody. We generally get along because I make sure to keep in my place: I am not a parent and make sure that his father is the authority figure. The problem is that his ex-wife thinks she can treat me like an unpaid nanny with zero impact or input.

I “can’t” schedule a family visit to my own home during her custody week and take my nieces to an amusement park. It is unfair to her son. I “can’t” say no to last minute custody changes like taking her son to an eye appointment while my boyfriend is out of town and she doesn’t want to. I “can’t” refuse

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