I think they are together (it wasn’t just mentioned properly), considering how sacha reacted when one of the aliens tried to touch gavin. Why would he worry?
They spent a lot of time together and sacha took him to that planet, just him. Maybe the author decided to leave it just for our imagination, “open ending”? Not sure if it’s correct in English..
so I decided to think they are dating! Coz who can prove the opposite? ╮( ̄▽ ̄)╭

This was honestly cute but i lowkey wanted gavin and sacha to be together but maybe im too greedy. i felt like the ending was rushed tho