You have very few options. Your best bet might be for him to stay in the house and keep the payments current. Then, when the market goes back up--who knows when that will be?!?, you can list it for sale and split the net proceeds or possibly he may then be able to re-finance.
Or, you could perhaps rent it out to a third person who will cover the cost of the mortgage and split anything paid in excess of the mortgage and expenses--again, that's probably not going to happen.
You could force a sale of the property by filing an action to quiet title in state court and both share in the loss.
I wouldn't suggest, based upon the limited info. that you provided that you just deed over the property to him. If you do that, you are still obligated on a house that you have no legal interest in.
It is never very smart, in my opinion, to do the last option, or as you are finding out, purchase a home with a boyfriend or girlfriend.
Sorry I don't have better options for you.