All The Things We Do For Money by MidnightSky

Sungyeol is a hot-headed teenager that finds himself booted out of his house by his parents. His life gets worse when his best friend demands to be paid rent if he's going to continue staying with him. One rainy night he meets business tycoon Myungsoo who makes him an offer he doesn't refuse, but soon wishes he had. Myungsoo is a young business man that has been treated wrongly in the past and is now slow to trust anyone. He uses Sungyeol to take his frustrations at the world out on, but he never expects what that choice will lead him too.

OMG the ANGST in this one! You WILL cry by the end of this, so be warned. CHARACTER DEATH! and :) and happy sappy moments and then more angst just when you thought everything was going to be alright.

I am not a huge Infinite fan, so I usually don't even read any of their fics. I don't remember how I found it, but it is one of my favs.