Should I keep the home or let it go?

I purchased a home with my father about 6 years ago. We always split the mtg 50/50. Once he retired about 2 years ago I told him we should sell since the market was still high and I was accepting a job offer elsewhere and would not be able to continue to pay my half of the mtg and a new home mtg. He refused to sell stating that he wanted to keep the home and would make the payments since he had a steady income(retirement check). Which he did for the last 2 years. Well he has just recently vacated, about 4 months ago, and has not paid a dime on the mtg. I have my own mtg and cannot pay for both. I have been able to pay half of the mtg which was my original amout. But our bank, a credit union is now threating to start the foreclosure process. Aslo stating that they will sue me personally for any owed money. I have kept my end of the bargain as far as payments go so why am I going to be penalized? And because of his nonpayment for his half of the mtg my credit is now ruined. My husband and I are expecting our 3rd child and need a bigger home (currently in a small 3bd condo). I do have potential tenants that wont be in till the next 2 months. But the bank is requesting a month and half of payment that maybe will stop the process. I was not able to rent it for the full mtg payment amount. I will still have to pay a difference but it wont be as bad as what I am having to pay now. So at this point should I try to save the home or let it go?