Jay and Hailey were just married in Season 9 so this inevitable breakup of Upstead will be extremely difficult. Once again, showrunner Gwen Sigan addressed the marital elephant in the room. When Jay is gone, Hailey will be “left in this, I would say, almost a vacuum, this emptiness of how do you move on? What the hell does that look like?”
Apparently, their separation will really take a toll on her job, which in all likelihood will put Hailey and others at risk.
Source: https://www.distractify.com/p/how-does-jay-halstead-leave-chicago-pd