I am the JustAnswer expert that will be helping you today. I am a lawyer with 25 years experience. Although I am not your attorney, I hope that I can give you helpful legal information.
Unfortunately the courts have consistently held that a transfer into a joint account converts separate property to marital property. However you have an argument that you are entitled to the entire amount remaining under equitable distribution
based upon the equities of the situation. Here is how it works.
Florida is an equitable distribution state. This means that in the event of a NY divorce the "marital property" is "equitably" divided by the court. Property that is "separate property" is not divided by the court.
Separate property (not subject to property division) includes inheritances, property owned before the marriage, personal injury awards, and gifts given to only one spouse UNLESS the property is transferred into both spouses names.
Marital property (subject to equitable distribution) is basically anything that is not considered to be separate property and most income and appreciation on separate property that occurred during the marriage. Income attributable to the efforts of either spouse is marital property.
An "equitable distribution" means fair, not equal although it often is. The court in determining what is fair looks at the duration of the marriage, the assets and liabilities of the spouses, the monetary and nonmonetary contributions of each spouse and any other factor that the court expressly finds to be relevant and equitable. Your argument could be that it would be inequitable for your spouse to receive any share of the remaining funds due to his mismanagement of the funds and the original source of the funds.
I hope that the information which I provided was helpful to you.
Best wishes for a successful outcome. If you have additional questions, please do not hesitate to submit them to me directly.