I'm not a vet. How can I qualify for 0 down on a home?
Depending on your qualifications, you may be able to get an MHFA first time homebuyer mortgage with little or nothing down. The payments depend on the sale price and mortgage amount. These days, they seem reasonable as compared to rent, but it depends on what you consider high payments.

What happens to the mortgage?
Put the home on the market and sell it. Divide the proceeds 50/50 or whatever you two work out. I assume you didn't sign an agreement before you purchased the home.