You will want to read your mortgage loan documents first to see how the lender addresses the death of one of the obligors - and do not default on the loan. Continue to make payments.
Often the estate of the deceased becomes the new cosigner on the loan.
I think you will want to speak to an attorney for advice on how best to approach the family of your ex-boyfriend and how best to remove yourself from the loan on what is now (more than likely) the daughter's house.