Jesse knew he was screwed, realized exactly where he had fucked up. What had originally started as an acting practice had quickly grown to legitimate feelings, which was going to make everything about ten thousand times harder when everything came crashing down around them, and more specifically around him. But he had made a promise to Ms. Corcoran, swearing he would follow through, and tried not to think about how much it would break Rachel's heart when she inevitably found out exactly what Jesse had done to her. How devastated she would be when she jumped to the reasonable deduction that this had always been a setup, that he never really had feelings for her, that she was just another girl when in reality she was anything but.
His plan was simple-slip into her room when she was still at ballet, put the tape in her tape player and hope she started it thinking it was something else. He wouldn't even have to face her and deal with the conflict of emotions he was trying to figure out. He had planned it well, and he didn't expect her to be home, much less to appear out of her bathroom while he was in her room. When she realized what he was doing, she protested, saying that she just wasn't ready for this yet. He assured her she was, and unable to help himself-he didn't have much restraint when it came to Rachel Berry-kissed her quickly, aware that it was the last time he'd be able to do so, aware that once she realized he was back at Carmel and therefore Vocal Adrenaline that she would hate him and she'd undoubtedly wind up back with Finn, aware that she would never look at him with her eyes wide and innocent and full of trust, even if she didn't.
He pressed play on the tape player on his way out the door, walking out quickly so that she wouldn't see how upset he felt. His show face was off, he couldn't help it-all the other girls he had been with over the years were just faces, names were rarely remembered, most of them were just using him for his popularity and talent. Rachel, on the other hand, was talented enough on her own that she wasn't trying to use him for his. And regardless of how badly she wanted to be popular, it was something she wanted to accomplish on her own without any help from others.
While their relationship was based on lies and ulterior motives underneath, he felt like there was also something real there-a real chemistry, a mutual respect and admiration. Something that, had they been given more time, could have turned into love and a support system as they fought their way to the top. Something that could have ultimately made them both better people.
Instead, he was forced to drive back to Carmel, forced to go back to his own show choir and in the end, forced to destroy the one girl he had ever even considered having a future with because he couldn't find another choice in the matter.