The story is nuanced and some people may not like dramas where the story is in the subtleties of two people in love, but that shouldn't mean it's a "boring movie" as someone else wrote. It's only boring if you aren't interested in the plot in the first place. For the rest of us, it's actually a little intense.
The interactions between the siblings are often only visual and without dialog. The barrier between right and wrong isn't really their concern, it's more about whether or not they can sustain their romance without having problems from the outside world. But see, they don't say these things, it is just implied. If you're not picking up on that, then I can understand why you would think it's boring or that there's no plot.
My only complaint is that I want to find out what happens next. I feel the movie could have been a little longer and have them run away together to try to make it work. The potential for a lot more drama is there, including how and where they hide, what they tell people about themselves, how long that lasts, etc. This film felt like the first episode in a series I'd like to see.
