What if you want a prenumpt YEARS before even meeting her. It's not something personal.
From my experience, I met someone once who I truely fell in love with. Thought I was going to marry her. She changed like a light switch it seemed like. From the coolest, most amazing chick in the world to this evil self-involved spawn of satan. To see someone change like that opened my eyes. I've also seen people with 40 years of marriage under their belt cheat on and then divorce each other.
I've just seen too much to put all my money down on a 50/50 bet when the bet isn't even required.
I totaly agree hearts change. IMO to really know a person it takes 2 years to build intimacy and trust. For the most part reasonable people will not turn to satan I know it does happen and sorry in your case it did. If it doesn't work then you move on and upgrade. I am positive there are millions of attractive bachelor adult girls in USA and I would say alot are attractive plenty fish in the sea.