I don't know as I can really be of much help with this. Relationships (marital or otherwise) aren't exactly my long suit, as we used to say. However here's a link to an article, from PC's archives, that discusses how to talk to someone who always becomes defensive along with a link to an article that talks about how to survive and thrive in an unhappy marriage:

How to Talk to Someone Who Always Gets Defensive

How to Survive in an Unhappy Marriage and Thrive

My best wishes to you...