Can I still claim my ex as a dependent? I moved out in October of 2023. I still pay for the full rent for her and my three children to live there.

[nicklas-krzyskow]

She collects ssi, but it was stopped in march of 2023 and she never held a real job.

[xmasbaby0]

No.    If  you did not live with her for the entire year in 2023 you cannot claim your ex as a dependent. 

It is not clear whether the "ex" is an ex-GF or an ex-wife to whom you are no longer legally married.   But....either way, you cannot claim her as a dependent since you did not live together for the whole year. 

Your other circumstances are unclear---we have no details from you regarding what you and the ex are doing about the children.   

[Texas Roger]

A spouse is never claimed as a dependent. If you are still legally married, you can file as married filing jointly or married filing separately. If you were divorced by year end, you must file as single. You may be able to claim your children as dependents. If they lived with the other parent more nights during the year than they lived with you, the other parent must allow you to claim them as dependents.