Coop has been putting all he can into running away from his troubles and the consequences of his actions in Your Friends & Neighbors, but it seems they've finally caught up with him in the recent episode of Season 1. One would think that getting arrested for murder and spending the night in jail would be Coop's worst nightmare, but at the end of episode 7 titled "The First Honest Thing," he says:
"That night, I managed to get some sleep."
It appears as if, now that the worst that could happen to him (getting arrested in front of the entire community and his family) had already happened, nothing worse could happen, and so he could finally breathe a sigh of relief and get a good night's sleep.
What changed for Coop at the end of Episode 7 in Your Friends & Neighbors?
Coop's assault in Episode 6 of Your Friends & Neighbors made Detective Lin even more suspicious of his involvement in the sudden onslaught of violence in an otherwise peaceful community. She gives him the opportunity to come clean to her when she visits him in the hospital, but he doesn't comply, insisting on his innocence.

Detective Lin's suspicions turn into something even more concrete when she finds a nanny cam in Sam's house, which has video proof that Coop was at Paul and Sam's place the night he was murdered, and that he's having an affair with Sam. She also finds traces of blood and ammonia at the crime scene, which points towards someone having cleaned up. She goes through Coop's trash to find his blood sample, and lo and behold, it matches the sample found on the crime scene.
These new discoveries, though circumstantial, are enough for her to obtain a search warrant for Coop's house. Detective Lin's suspicions are helping her slowly build a case against Coop. However, they turn his entire house upside down and fail to find any incriminating evidence.
Your Friends & Neighbors has been subtly foreshadowing that Coop's car's trunk opening up automatically is going to get him into trouble, and that is exactly what happens. The officers find a gun, the murder weapon, inside his trunk, which has once again, popped open all by itself.
Finding the murder weapon inside Coop's trunk was more than enough evidence for the cops to arrest Coop, in an albeit dramatic setting in Your Friends & Neighbors, at Paul's funeral in front of his entire community and his family. Coop blackmails a lawyer to fight his case, but the weight of the evidence that the officers have discovered prevents her from getting bail for Coop, forcing him to spend the night in jail.

One would think that after everything he's done to avoid getting caught, Coop would be spending the night panicking and breaking down, but to everyone's surprise, he makes himself comfortable in the prison cell and gets a good night's sleep. This might be because, from Coop's perspective, the absolute worst that could happen to him has already happened.
Now that nothing worse can happen, he doesn't have to fear anyone anymore, and so he is free, calm, and collected, for the first time in Your Friends & Neighbors, and ends up getting a good night's sleep.
Only time will tell if this was the worst that happens to Coop in Your Friends & Neighbors, as two more episodes are left before this season concludes.
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