I went through a nasty divorce sometime ago. I remarried recently and my husband and I just bought a house. We put equal amount of money in it. Right now we are thinking of doing some remodeling and addition to the house. We don't have money for that. However, I can sell my condo I bought prior we got married. But I learned from my previous mistakes and in case something bad happens and we got divorced, here in California we'll have to split house equally, no matter how much more money I put in it. So my question is can I do something like prepare a paper saying that in case a divorce I get my remarriage money back first and after that we share equity, if we have any. And make my husband sign it. Thank you so much!

Look into a postnup.
Or better yet, see if you two can get a home equity or renovation loan in both names, of course.
I kept my premarital house and 24 years later I am happy I did.