Wow, so many people hate Bennett. Honestly I never saw him as anything like a creepy stalker or anything near spoiled. More like he has low self esteem
Back home he's just that weird kid that stays locked up in his room studying bugs. His own mother constantly acts like he ruined her life, his father is dead or left, and he can't even bring himself to ask out the cute girl that moved in with him. Notice when Luna left the mansion he knew where she went, but he didn't stalk after her like a creep. He stayed home.
Then one day things changed, a man named El came to visit and for the first time someone saw potential in him. He said he has what it takes to be in the E4. He finally feels like all his hard work is starting to pay off. And when this El guy claims to be Luna's dad, how could he distrust him? Even Adrienn was fooled into believing El was a kind person and xe isn't any fool no more than Bennett is.
Next he hears the girl he likes was hypnotized by radomus. Why wouldn't he help El get her back to safety? Given what he knows it's the right thing to do. Granted he has probably has no idea what El is going to do. Once the "ritual" started Bennett was no doubt starting to rethink things. But what could he do? He was surrounded by cultists and El was the only person who was ever kind to him. Regardless after Luna is freed he even followers after to try and apologize and finally come clean on his feelings.
Then, he gets rejected flat out. She leaves. But after finally getting enough courage to ask her out he can't just give up immediately. After all he's grown so much. Maybe if he could talk to her one more time. So he battles you, not just to get the key but to show the fruits of his labor. The person he last battled before his training was you after all. But in the end, he still failed.
How could this be? He thinks. Haven't I improved at all. Am I still just that same old bug geek? He states how stupid he was for thinking he could change. Finally he decides the only thing left to do is to go back to the only person that believed in him. To hone his potential El saw in him.
He doesn't state he's going to force Luna to love him by becoming an E4. He says he's going to prove everyone wrong. And that he's not just a geek or the kid who ruined his moms modeling career. He's angry at everyone looking down on him.