With this Witch by Isla Winter (Leeside Witches book 1)

A marriage of convenience proves to be magically inconvenient, and no spell will get them out of it or calm their burning desires.

Being a legacy witch comes with expectations, and, unfortunately, when Gammy shares that she’s sick, Petra becomes the front-runner for the role of Premier Witch, a part she’s never really wanted. The inconvenient catch? Traditionally, the Premier Witch must be married, and a combative supernatural council member is only too happy to point out. Petra must now find a husband to prove she is serious about accepting the role. Oh, and she must do it in the next thirty days! If she fails, she loses everything.

Enter bar owner and current delicious demon representative on the council, Lachlan Grace. A close friend of Petra’s, Lachlan, has been drawn to her from the moment she walked into his bar. Battling his own demons from his past and tired of being just friends, Lachlan offers himself as an option for a marriage candidate. Will he be able to move out of the friend zone while also keeping his history in the past?

Now, thrust into supernatural politics with a looming deadline, Petra finds herself questioning what she wants in life, struggling with how to make her Gammy proud and keep in check the pesky feelings bubbling under the surface for a smoking hot demon at the same time. What’s a witch to do?

Tropes you'll find:
Marriage of convenience
forced proximity
Witch/Demon
Fake dating