HI Jenny,
Just to throw my 2cents in, I do think you need to inform your future mate well before being too serious. And yes people do change their feelings after a while. I told my second wife just as soon as we started getting serious. And now even after we've been married, when she starts to worry a bit about it, she remarks to me, well its not like you didn't tell me from the start. Then we talk some more about it and I give her more assurance.
One thing that helped my wife from the begining was that I was doing volunteer work, helping paraplegics, and she watched me from a distance. She saw my heart, and said to herself, this is the kind of man I want to be with. (She related all this to me later)
So when the time came when I gave her the, "there's something about me that you need to know", she was willing to work through it.
bless you