Sweet & Bitter Magic by Adrienne Tooley

Tamsin is the most powerful witch of her generation. But after committing the worst magical sin, she’s exiled by the ruling Coven and cursed with the inability to love. The only way she can get those feelings back—even for just a little while—is to steal love from others.

Wren is a source—a rare kind of person who is made of magic, despite being unable to use it herself. Sources are required to train with the Coven as soon as they discover their abilities, but Wren—the only caretaker to her ailing father—has spent her life hiding her secret.

When a magical plague ravages the queendom, Wren’s father falls victim. To save him, Wren proposes a bargain: if Tamsin will help her catch the dark witch responsible for creating the plague, then Wren will give Tamsin her love for her father.

Of course, love bargains are a tricky thing, and these two have a long, perilous journey ahead of them—that is, if they don’t kill each other first.