The key to having a successful short sale is lender approval. Lenders usually have a short sale package, included in that is a request for a letter of hardship. A hardship usually means that some terrible happened to cause you to no longer be able to make mortgage payments.
I am not sure that just because you two broke up and moved the lender will understand that to be a hardship. Life happens, this does not sound like something that would rise to that level, but try anyway.
There are people who think that any circumstance will qualifu for a short sale, and that is not the case.