Are you the student, or is your son?
If you are the student, you will have to find a public flagship that is affordable for you. You can submit the FAFSA application, but know, going in that it takes everyone’s income into account.
If the funding is for your son, the stepfather’s income will be considered because you are married.
Remember that the Free Application for Federal Student Aid is just an application to see if the student qualifies for the paltry aid the government provides. (Pell grants are ~$6K per year/Federal loans start at ~$6K per year). Not a lot of money to fund a full college tuition.
The application is then forwarded to the schools, which is where the actual, decent, funding is dispersed.
The government and schools don’t consider whether or not your spouse chooses to contribute. It doesn’t matter that you are “low-income” and your husband is not. If that were the case, everyone would say that they chose not to contribute to their family’s college costs.