I didnt even see Bellamy as that much of a jerk in the beginning. After the pilot I thought he was kinda douchey but he honestly wasnt even in the episode that much? 102 I loved him.
It was obvious he was mostly bark and no bite and wasn't really going to hurt anyone. And it was obvious that deep down he really did have a good heart. And it shifted pretty quickly. IMO he was mostly misunderstood more than anything.