Ask an attorney ASAP ...no one here, especially RE agents, can answer. Too may variables and legal issues. It may be counted as a marital asset during divorce procedings and therefore negotiable in the settlement (if you pursue a divorce).
If the deed has your name on it then you are the owner. Having the mortgage is the bad side, having the deed is the good side. I would suggest speaking to a lawyer since I don't know the NJ laws. Was there a separation agreement and did it give you the lot? If so you can sell it, since the mortgage is in her name she would have to hope you would pay it off for her, again speak to a lawyer.