What do you mean by "claim him"? You cannot claim a spouse as a dependent. If he had earnings for 2024 before he went to prison, then if he agrees, you can still file a joint 2024 tax return. Or....if there are children and you have lived apart for at least the last six months of 2024, you can file as Head of Household and enter just your own income and the information for the dependent children.
This assumes ,of course, that you are in a state that recognizes common law marriage:
STATES THAT RECOGNIZE COMMON LAW MARRIAGE
CO, DC, CO, IA, KS, MT, OK RI, SC, TX, UT
**Disclaimer: Every effort has been made to offer the most correct information possible. The poster disclaims any legal responsibility for the accuracy of the information that is contained in this post.**