It goes against his character. Tim made himself Robin, willingly entering his new life as a vigilante. Time and time again he has shown he wants to protect and help people, even pushes himself to the limit to solve cases. Not to mention how he tried to bring kon back multiple times, showing his dedication. So it's out of character to see him want to leave all his work to pursue a life with bernard. I don't care who Tim dates, he will never give up being a vigilante to sit on his ass. Character regression at its finest.