sex in this movie?

There's no sex, only kissing, and implied sex.

There is a masturbation-scene but you only see Agnes hand go into her pants while she's looking at Elins picture in the yearbook and then it kinda switches to her fantazising about snuggling up to Elin in the school cafeteria.

There's also a brief post-sex scene with Elin and Johan if memory serves me right or they only reference it I can't really remember which, but again nothing explicit.

Light travels faster than sound,
that's why people seem bright,
until you hear them.

This movie isn't about sex, it's about love.