Your situation is not uncommon. If your wife would not sign a Joint Petition to Remove Condition to Permanent Residence, then you may file an application to WAIVE the joint petition requirement based on a hardship of three kinds:
(1) extreme hardship would result is such alien is removed from the US;
(2) the qualifying marriage was entered in GOOD FAITH by the alien spouse but has been terminated (other than through death of the spouse) and the alien was not at fault in failing to file the joint petition and attend interview; or
(3) the qualifying marriage was entered into in good faith by the alien spouse and during the marriage the alien spouse was battered by the US citizen spouse and the alien was not at fault in filing to file the joint petition and attend the interview.
A proof of "mental cruelty" is a tricky issue because you have to provide enough evidence that you were mentally abused.
