The best standalone

Such a sweet Romeo loves Romeo book! The two families have a very long history with each other and hating eachother.. but one night one of the men gets back from a 6 year trip in London and finds a handsome man who is attracted to him and they start to kiss. It turns out that man is his enemy and they had no clue. Through the entire book the men are finding a way to be with each other and working through the feelings they have about *betraying* family by being in love.