A pre-num is not a bad thing. I would not get married without one, and I am not a wealthy person.
It depends on how it is written, but does not mean that he is going into the relationship expecting divorce, nor does it mean you will come out penniless.
It is like an insurance policy. You don't plan to have your house burn down, but take out insurance because the concequences if it does are catastrophic.
Same with a pre-nup. With divorce rates running over 50% it just makes good sense. None of these people go into the marriage wanting a divorce, but sometimes they are out of your control.
The pre-num does not mean you will be out of pocket, just that you cannot rob him if things turn sour. Your honey has worked hard/inherited all his money and he should have the right to keep it if you vanish with the pool boy.
Make sure that while you are together, you get an equitable share of what you put in, and you will be right.