Several years ago I separated from my wife but the divorce has now gone through. I still own half of the marital home but I have been living in rented accommodation since the separation. Can I claim that my old marital home is still my main residence for capital gains tax purposes when it is sold?

I intend to remarry and my girlfriend wants to give me a share of her current home after we are married. Apparently this was let for a time before my girlfriend made it her home. Would there be any capital gains tax advantage in doing this?