Why don't they make it clearer that this is aimed at 12 yr olds?

I went to the cinema expecting a mature and interesting romance story. Instead I got a flimsy story about 2-dimensional cliches with no emotional honesty whatsoever.

Lou felt like a teenagers version of Sally Hawkins character from Happy Go Lucky, with nowhere near the subtlety or complexity. The relationship to Patrick was embarrassing in places, their complete lack of communication, honesty, empathy or integrity despite being together 7 years? Again it was like a teenagers idea of a failing relationship. Lous family was always upbeat and supportive despite the obvious pressures, in a way that felt more like a Richard Curtis film than anything real. Will was such a cliche, and so badly written to be always just smugly depressed rather than genuinely bitter (ie afraid/hostile) or compassionate and shame-stricken. I have no idea how Jojo Moyes ever had this story published let alone made into a film, it feels like something a naive and inexperienced teenager might write.