I don't believe Sakura deserves a happy ending. The way I hope it happens is that she catches or becomes aware of fuckboi sleeping around and confronts him. He gets pissed and drops the act with her and then she starts to get dropped by her agency down the relevancy pole. And then she gets involved with the scummy side of things with directors and executives. Maybe at the end of the story she leaves the industry or finds a small time part where she's somewhat happy and not being taken advantage of, but she can't have big success.
Shinobu needs to move on with Fumi and let himself be with someone who actually loves him and won't betray him.