Ex refusing to pay her half of the mortgage payments while we are trying to sell the house

Location: Missouri

My now ex and I purchased a house in Missouri in 2021. We were never late on a payment the whole time we've been here. Things happened, fell out of love, she moved to Colorado with her new girlfriend.

She was here last month packing all of her things, left a bunch of garbage that I had to toss. Realtor that she picked did a walk through and told me a bunch of other things that need to be cleaned up before she comes to take pictures.

My ex refused to pay her half of utilities, so I paid them. I have to use my own money to get the house cleaned up for the sale. She's now refusing to pay her half of the mortgage payment. My loan agent told me that if the payment gets hit with a late fee, it will affect my ability to get a loan for a new place, but I don't have the extra money to pay her half right now. The realtor told me to get in contact with a lawyer, but that's going to cost money that I can't spare, the money from the sale is supoosed to be my down payment on whatever house I'm going to be moving to. What can I do?