My thoughts are similar to Anvil's...I wouldn't like it if it were me. How about if he sells HIS, put the proceeds towards yours, and helps pay it off sooner?
The level of caretaking/controlling/urging is raising some hairs on my neck... Maybe for no reason, but it doesn't feel healthy.
It could be "innocent" codependence, not setup for abuse down the road, but that still seems like a recipe for danger.
This is coming from someone who has offered similar help out of love before (of course I want to give!) and realized it wasn't the healthy thing to do, especially in building a partnership.