Your husband lost his job, so you don't have enough money to pay for your home loan. Now you're trying to sell your house. You explain why you're selling it to a potential buyer:
We're no longer able to afford the mortgage payments.
This phrase describe something that you used to be able to do, but can't do now.
"No longer able to ___" sounds pretty formal. A more casual, conversational way to say this is:
We can't afford the mortgage payments any more.
This means to have enough money to buy something:
We can't afford to send our kids to private school.
A "mortgage" is a loan that you get in order to buy a house. When you get a mortgage, the bank technically owns your house until you finish paying off the entire loan.
The money that you pay the bank each month for your home loan is called a "mortgage payment".
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