You might want to look into a "Change of Circumstances"?
Check out some of my earlier posts. My ex is is living with another guy, and they are buying a house together. They are not married, and as far as I know, are not in a domestic partnership? I am considering the same issue; Modification/Termination of Spousal support
Ummm this does sound like to me a major "Change of Circumstances" and could be brought to court to maybe have the spousal support reduced or terminated?....I'm not an attorney, but I think some of the other people here will chime in here, and give you some worthly advice.....?