ADU's can be rented to anyone whereas Family Member Units are only for persons related to the property owner by blood, marriage or adoption. 

keep in mind, its a marriage, and if it goes bad, its a divorce, so plan ahead.

Look at the partnership as a marriage if you will.

@Aaron Mikottis Congrats on your marriage!

His success in his marriage and raising kids?

Congratulations on the marriage!

Why on earth would someone prioritize the quarterly profits of Capital One over their own marriage?

I always thought of cohabitation as a man and woman unrelated by blood or marriage living together.

Even though we don't get along in the marriage we are still good friends.  

Before same-sex marriage became legal across the land, some states (MA, NH, DE specifically, I think, but I could be wrong) enacted legislation to protect unmarried same sex partners in this exact situation and it applies equally to unmarried hetero couples as well.However, children - particularly minor children - have some protection here as well and a court would not necessarily ignore them in favor of an unmarried partner, particularly if the house was the sole asset of the decedent.A married spouse usually receives all assets of the decedent and if the girlfriend can claim common law (or if it was already established prior to his death) through the state they were living in, she could receive it all.That said, I do not believe the mortgage company will permit a dead person to remain on a mortgage once probate is settled, so the house would have to move into a trust or to somebody else's name and the ex-wife would then be able to remove her name from it and move on.So yeah - I'm thinking out loud, but the above are all issues or question I would ask a SUPER COMPETENT attorney.