My ex quit claimed the property to me but he is still on the mortgage.
Accepting real property via a quit claim deed is perilous at best.
I would suggest, if asked, never to convey (or accept such conveyance) property via a quit claim deed.
The preferred conveyance (in my humble opinion) is a warranty deed.
A quit claim deed purports to convey the owner's total interest in the property, however it contains no warranties regarding the title.
That is to say, there is no assurance that the title the owner holds is valid and marketable.
That means that the deal only transfers whatever rights of ownership that the seller has at the time of transfer.
I could sell you my interests in a property for $500 via the quit claim process.
If I had NO valid ownership interest in the property, that is what I'd be selling/scamming you for $500.
As you've now learned, the quit claim deed has created additional issues for you.
Banks (and other lenders) won't finance real estate if the conveyance used can't prove a REAL interest in the property "free and clear" of encumbrances.
You might wish to visit a couple local real estate attorneys to discuss the path forward regarding the home you thought you could procure.
It is very doubtful that internet discussion boards will be of much assistance you regarding complex legal matters.
I wish you all the best moving forward.