One additional thought.
There are fiances and fiances. By that I mean there are people who use this term to signal a committed, exclusive relationship; people who use it to mean we intend to get married at some vague not yet agreed upon time in the future; and people who use it to mean we have a fixed plan to marry within the next year or so.
(I had the startling–for me–experience of having one of my neighbors who is 65+ tell me she had gotten engaged and showing me a beautiful expensive engagement ring. When I asked when they were going to marry, she told me they were never getting married. She just wanted the ring and having the man she is living with give her the ring and introduce her to her friends as his fiancee was something she saw as proof of his commitment. I don’t get it…but I don’t have to if she’s happy.)
Be aware that some of the things that can be done to protect your D in this scenario will be rendered null and void in most states when the couple marries UNLESS there is a prenup. You should also be aware that there are certain advantages to a “tenancy by the entirety” --something only married couples can have in most states and which you may not be able to get if you protect her contribution too much. So, ask the lawyer who helps you draft whatever you agree upon whether it will still be valid after they marry if they do.