Which chapter are you in now?
He didn't rape her. The sex was consensual, although he, apparently, was so inexperienced
and selfish that he was really rough, resulting in Bai Xiaonian not enjoying her first time at all. After they were done, Lu Jinnan went to his car to fetch a bottled water for Bai Xiaonian, leaving her alone in that old building. To Bai Xiaonian's surprise, Lu Jinnan's enemies were there the whole time. Yep, the two had unknowingly performed a live sex show for other people. So, in that short moment of Lu Jinnan's absence, the enemies threatened Bai Xiaonian that they would hurt her and force Lu Jinnan to break one of his legs. When they tried to grab her, Bai Xiaonian got a scare and decided to jump off the building, thinking that two stories wasn't high. That's how she ended up being in the hospital.
Bai Xiaonian and Lu Jinnan started having feelings for each other after both of their fathers, coincidentally (and conveniently), were hospitalized and occupying the same ward. They first squabbled a lot, but each of them soon realized his/her own feelings for the other.