I agree with the others. It does not seem to be equitable that he thinks you should credit him for $19,000 for the upgrades without crediting you with an offset for your down pay contribution. There may be more math involved, so I won't render an opinion on why he would feel entitled to it. If your home has no equity, or negative equity, it makes no financial sense that he would make an issue of this with you.
An illogical demand from him such as you described sounds like the emotional grudge of a man in pain, or a man wanting to cause pain. He needs counseling, but you can't suggest that. He wouldn't take that kind of advice kindly from his opponent in this "War of the Roses".
Also don't know how use of your premarital funds would be handled as that depends on specific facts (i.e., can you prove that those funds were your separate property or did you commingle?). Like I said, I would highly recommend that you consult with an attorney before you sign any loan documents relieving your husband from the loan obligation. If you don't have an attorney already, you may want to consider a Legal Shield membership which entitles you to consultation with an experienced divorce attorney on unlimited number of legal issues. The monthly membership is very affordable ($17 - $26 depending on which plan you choose).
With all those unanswered questions, it seems like signing refi docs may be premature. Get satisfactory answers before you sign.
Anyway, I am not an attorney. If you need legal referrals, please feel free to email me and I will send the information. Thanks!
Hope this helps!