Should I go or not go?

So my twin sisters baby shower is August 1st. Her husband is best friends with an EX on mine. That’s how we met. His best friend is going to be an “uncle” to my niece. My husband is not comfortable with me and my son going to the baby shower due to my EX, my husband works on that day and we REALLY need the money. My EX and I used to talk off and on before my husband and I got married. Should I go to the baby shower and upset my husband? Or not go to the baby shower and upset my sister?

Before they invited my ex they knew it would make problems in my marriage.