Alimony is based on need in a lot of cases. However, your marriage is considered a short term duration and you actually never depended on your husband for income from what you are saying. I suggest you file for divorce and ask for rehabilitative alimony. This would allow you to go to school and be trained for a career. I am not saying you will get it but certainly worth a try. Contact my office for an appointment.
My colleagues are more than correct. In order to really work this out, you need to hire an attorney who can prepare an equitable distribution of the debts. I hope that you have assets that can be sold and divided otherwise you will have to depend on a decision by the court that if your ex wife to be is to be responsible that she will pay her half . Unfortunately it looks like you signed for the loan. I suggest you see if you can recall any of the debt if your child has not yet started...
The court will impute an amount or may use the income average for the past two years as a start point. As to sole custody, is that something that you agreed on. Today the court calls our child system "time sharing" - there is no longer a primary custody. There is a parenting plan on the florda family law self help page that you can review.
It does not appear from your statement that she is stealing your mail - rather she is sending it to you. The fact that she opened it does not necessarily mean that she is violating any rule of law, it could be a mistake. I suggest you file another change of address notice and also contact those known to you that would be sending you mail.