This is War by Kennedy Fox is the first book in their Checkmate Duet. A straight up childhood acquaintances to enemies to lovers story, the enemy part will crack you up with the internal monologues and vindictive glee. Viola Fisher has crushed on Travis King, her older brothers best friend for the longest time, but now? Now she hates him, loathes him, cannot stand him AT ALL. Travis has pushed away Viola, she is forbidden, not allowed, his best friends little sister. He has successfully managed to make her hate him, perhaps a little too well. 
 (Side note, him man whoring to push her away reminded me of Kellan Kyle from Thoughtless when he was trying to push Kiera away. At least, it kicked up the same angsty feelings on my end.) 
 As this is a duet, it has a cliffie ending, but fear not, This is Love should be out soon.