When my husband and I got married at 20 we didn't have a pre-nup because quite frankly we had no money or assets. After 22 years of marriage everything we have we've built together.
If for some reason I found myself in a situation where I was getting remarried (a good friend of mine lost her husband so it does happen) I would probably ask for a pre-nup. NOT because I didn't trust the person or think the marriage would last (I wouldn't get married if that was the case) but because I have two children to consider.
Anything that was earned within the second marriage would belong to the second marriage but protecting the assets that were earned with my children's father would be my priority. If something were to happen to me and/or God forbid the marriage didn't last I would want to make sure that my children received those assets.
I don't know much about your situation but if this is a concern I would suggest discussing with a lawyer. If there are children involved you would probably want to considering establishing a will, POA for health and finances, a trust, etc prior to the marriage. Discussing finances prior to committing yourself is critical. Finances can put a huge strain on a lot of marriages.