If I buy a house while we are separated but still legally married, does he have any rights to that house? Is there anything I would need to do to ensure it was my own property and not tied to him?
Yes, there are certain inchoate rights that can attach to any real property you purchase prior to divorce. An executed Separation Agreement and a Memorandum of that Agreement recorded with the register of deeds in the county where you purchase land will cut these rights off, a Free Trade Agreement will do the same.