I Love You (The Portals, Book 1)

Newra and Jonas had just become a couple when Newra wakes up to find a portal in the wall of her bedroom. A girl claiming to be Jonas's 'female self' from another universe says that she needs help because her boyfriend and the rest of her world were captured by invaders from a parallel universe.

If her universe is not saved, then everything they both know will be exterminated.