I am also very sorry for what you are going through.
I just wanted to tell you that my friend went thorough a similar situation.
Something happened to her FH just as they were about to mail out the invitation. He became very distant and she knew something was wrong. They talked about things and he told her that he didn't want to get married. She was devastated at first.
But she knew that he was the one that she was supposed to spend the rest of her life with. They spent a few days apart, thought about things and finally talked things through. They ended up postponing the wedding for a year and they are now expecting their first child.
So ultimately, if you feel that he is "the one" take some time, think and talk to each other.
I hope everything works out for you!!