I get what you mean by "mature" but they tend to have sad/ unsatisfying endings as thy mimic real life- and real life isn't happy all the time.
Two Lights: Relumino is a short and simple kmovie that I would recommend.
You are kinda asking for the impossible as dramas need drama in the story lol So yea a couple meets and falls in love but there has to be some kind of rift between them. Its gonna mean they are apart for some reason and get back together later or the ending isn't gonna be a good one.
I personally would like to see some recommendations myself from others of what you're asking for...