So obviously Wren and Eddie’s relationship was extremely strange. We know Eddie was wary of Wren because he found out Wren was supplying CeCe with visitors passes.
What I don’t understand is…
…if CeCe was already a patient at Radley, why did she need visitors passes in the first place?
Wren tells Spencer CeCe contacted Melissa about helping Mona. He claimed that CeCe offered help because she had been through torment inflicted by Alison (being kicked out of school) and wanted to help Mona recover from her past with Ali. We know this is a lie; CeCe was actually being helped by Mona to learn more about the girls.
This leads me to believe that the visitors passes issue was not the true reason Eddie disliked Wren; it makes no sense.
“… from the minute that guy got here, it wasn’t for the right reasons.”
Was his reason that he needed to keep his enemy close? Maybe Eddie noticed Wren was treating CeCe differently than other patients and was concerned by it.
Eddie may have noticed Wren and Mona’s strange relationship too. As we know, Mona was helping CeCe, and it seems Wren was working against her. Mona and Wren’s famous conversation implies that Wren was interrogating Mona in order to uncover the truth about Wilden’s murder. His actions in 4x10 caused CeCe to become a person of interest in Wilden’s murder case. Therefore, Eddie’s concern over Wren’s true intentions may have derived from his involvement with Mona. He might have realised Wren’s “therapy” sessions were more like interrogations.
Eddie’s disappearance may not be irrelevant either. Assuming Wren is definitely working against CeCe and Eddie was interested in why, Eddie may have done some investigating and found out the truth about CeCe.
Before we knew CeCe was A, Wren theorists believed Eddie found out the truth about Wren being Charles. He made Eddie disappear so he wouldn’t tell anyone and ruin his plans. Maybe this idea still applies, but instead, Eddie found out about CeCe’s past and her being A through Wren. CeCe got rid of Eddie so that her secret wouldn’t be revealed.