I agree with those above who say that their impression of the theme of the stage musical is nothing like, "Don't be like Evan." It's almost the exact opposite.
When I saw the show during Broadway previews, I was really surprised that the writers had Evan have what is presumably a sexual relationship with Zoe under false pretenses. They could have put in some throwaway lines of someone saying something about his or her reluctance to do so but they didn't. The Harvey Weinstein allegations that brought the #MeToo movement to the forefront didn't happen until almost a year after the Broadway opening. If the show were being written today, I don't think the writers could have brushed off his behavior as much as they did. I have not seen the movie, but apparently the consequences to Evan for his behavior are much greater.