Husband going on vacation with his family and didn't invite me?

This morning my husband mentioned that him and the baby would be going out of town with his family for a reunion and to go to mt rushmore...(his family has been talking about this for a while) we decided we weren't going because we don't have the money...but this morning he said we are going with them and you can't go because you have to work...I work at walmart making 9 dollars an hour and i work 4 hours a day I think i could have arranged for the day off...not to mention it's not for another month...Why wouldn't he want me to go?? We never go anywherer together...