Someone Else Has Access to My iMessages

In October 2023, the individual that I was in a relationship with was given access by me to my iCloud account on his iPhone for emergency reasons. After he did what he needed to do, he logged out of my iCloud on his phone. We both purchased new phones since, however, he has access to my iMessages because they upload on his iPhone. I’m not sure how this is possible and I’m assuming it is because he was once logged into my iCloud on his old phone and maybe our iCloud accounts merged. I confirmed he does in fact have access to my messages and my Apple wallet on his iPhone. I do not want him or anyone else having access to my iCloud information. I’ve already checked my iCloud account to confirm what devices are registered and it’s only my devices. I’ve also changed my iCloud password and that didn’t work. Is there anything else I need to do to ensure he does not have access to my iCloud information?