The Summer of Us by Cecilia Vinesse

Five friends. Five cities. Two complicated love stories . . . The perfect read for fans of Jennifer E Smith and Sara Barnard.
Aubrey and Rae have been planning their European tour since the moment they met. It was meant to be the perfect way to spend their last summer together before university, but now it's not just the two of them . . .
There's Jonah, Aubrey's seemingly perfect boyfriend, and Gabe, who Aubrey may have accidentally kissed. Then there's Clara, the friend Rae is crushing on, hard, even though there's no hope because Clara is into guys, not girls. And on top of all that Aubrey and Rae's friendship appears to be falling apart. Things are more complicated at eighteen than they were at ten.
Set off on a romantic adventure that embraces warm summer nights, the thrill of first kisses and the bittersweet ache of saying goodbye to the past.