Beautiful Disaster by Jamie McGuire
Travis Maddox, on the other hand, is nothing like good girl Abby. Travis is a college bad boy covered in tattoos, in hangs with a rough crowd and is the campus charmer that has all the girls swooning over him. The two finally meet when they realize that Abby's best friend and roommate, is dating Travis's best friend and roommate. While Abby does not care for his lifestyle or bad boy charm, Travis is turned on by her resistance.
Hoping to finally get the point across that she is not interested, Abby agrees to a simple bet brought on by Travis. If Travis wins, Abby must live with him, in his apartment for a full month. If Abby wins, he must refrain from sexual contact with other girls for a month. Either way, one of them is going to be in for the longest month of their life. Travis has unknowingly me someone he can't beat, and someone who won't stand down in fear of his bad boy ways, and someone he can't intimidate.