Jesse really hadn't meant to fall in love. It just wasn't something he did. He had certainly not meant to fall in love with the wrong girl. He had been sent to McKinley for Rachel Berry, but he stayed for Quinn Fabray. At first, he had done what he was supposed to. He had gone and seduced Rachel, and then when that had posed too easy a challenge, he broke up with her. Shelby had sent him to tell Rachel that she was her mother, and he had done that. But since he was there, he might as well give Vocal Adrenaline even more of a competitive edge by making sure their only 'competition' (he used the term loosely) wouldn't be in the state to compete at Regionals by ruining their team dynamic and leaving before it was too late.
In his opinion, it was foolproof. He had done plenty of people studying while he had pretended to be Rachel's arm candy, and he had noticed a certain person who seemed to have a relationship with every other person in the Glee club – a blonde ex-cheerleader named Quinn Fabray. It seemed that if he were to pursue her, it would affect several key members of New Directions. It would certainly hurt Rachel, as he had spent many hours listening to Rachel go on and on about how Quinn always got what Rachel couldn't have, and from these rants, he had picked up that the blonde had dated not only Noah Puckerman, one of their best backup male singers, but Finn Hudson, their key male singer (after Jesse himself, of course). Stirring up these three key points would definitely hurt the rest of the team, as sides would be picked and divisions would be made. He was a genius.
However, what he hadn't planned on was actually falling for the girl. He had expected her to fall for all of his tricks, just like every girl before her, but she hadn't. Every time he tried to smooth talk her, she just gave him that expression, the one arched eyebrow and the gaze that read 'please continue, I am so thoroughly entertained' that not even he could resist. Every time she would just give him that small smile and say, "thanks but no thanks, St. James," before turning on her heel and walking away. It was both infuriating and intriguing.
The first time she actually responded positively it caught Jesse completely off guard. He had expected their usual routine: he would ask, she would say no, he would say 'one of these days, Fabray,' and she would reply with 'maybe, St. James' before walking away. This time, however, she said yes. She had given him a soft smile and replied with 'I'll see you at my house at seven,' her smile growing into a grin as she realized she had definitely caught him off guard, and he had managed to stammer out 'see you then' before she left him alone in the hallway.
However, just because she went on a date with him didn't mean that she was ready to completely give into him. She still played her games with him, occasionally turning his offers down and telling him that he was 'just cute' before giving him that maddeningly attractive smile, or watching him during a performance with that one eyebrow arched expression he had come to know meant she really was interested. And for some reason, Jesse was okay with that.
