An individual must ask for removal of the conditions of their residency jointly with the spouse who petitioned them if they are still married (unless there has been abuse) OR they can ask for removal of the conditions without the spouse if they are divorced at the time the I-751 is filed. A separation is not enough, there must be a divorce. In order to receive approval of the I-751 you must show that the marriage was a real marriage (not just based on immigration status) at the time you were married. If you have remarried, this will make immigration look even closer at the first marriage. Your I-751 must be approved, you cannot simply rely on the second marriage to start the process over again. I strongly recommend that you consult with an immigration attorney to assist you in the remaining process you have with immigration.