They haven't gone back to the beginning. The officer knows that they are connected to the murder (even if he isn't an officer anymore) and Sangwoo has what can be described as a lust toward Yoon bum. It may not seem like much, but on a psychological level, we can predict big changes in the upcoming season
He has had his suspicions since the first chapter and still doesn't have any evidence. Him not being an officer means any evidence he does gather would be through illegal means thus inadmissible in court. But lets hope there is a slip up somewhere.
As for the psychological development I would call it more an obsession than lust and that's because no matter what he does Bum keeps saying he likes sangwoo. Lets hope you are right about the changes. Or this story will lose its charm. For me atleast.
WTFFFFFFF.......