If my girlfriend of 18 years is in a terminal stage of liver failure and we have a joint mortgage and bank account, what do I do?

You, and more importantly her, need to see an estate planning attorney asap.  A joint mortgage implies that both of your names are on the Title to the real property but doesn't say how - tenant's in common?  Some sort of joint tenancy?  Unless she already has a will providing for you, nothing she owns is likely to go to you and you can find yourself owning your real property in combination with someone else that you had no intention of investing with.  Check with your bank but most joint bank accounts (assuming you mean joint ownership, not just that both of you have signing rights on the checks) will automatically belong to the survivor when one owner dies.  What about her personal property? Who will have the right to decide funeral, burial, and other such rights?  Unless she jumps through the proper legal hoops before she passes, it won't be you.  In most states, you will have absolutely no rights to decide anything dealing with her remains, her property, or her estate in general - marriage does still make a difference in some contexts.  Perhaps most important of all, who has the right to direct her medical care and make decisions for her if she is no longer able to do so?  It won't be you unless she makes provision for it while she is still mentally able.  It may seem obvious now, but there are countless examples of estranged family members swooping in at the last, taking charge, banning the significant other loved one from even seeing the person, let alone having any input or even information as to what is happening.  To the extent you live in a house that she owns, you can also find yourself being evicted shortly after she passes.  All these sorts of grisly scenarios can be avoided with a bit of planning and executing the right paperwork - but that has to be done while she is still able.  So see a probate or estate planning attorney.  Now.