Disclaimer: I don't own any of the characters of Glee.
Take it to Heart
In the beginning, his reasoning seemed perfectly legit. He'd slowly get back with Santana and by the time he had "broken up" with Quinn she'd go back to Finn and they'd have their Puck-less happily ever after plus one. Finn and Quinn would be happy, since Quinn obviously chose Finn from the beginning, and Puck...well, he'd tolerate it. Besides, he'd have the equally bitchy Santana fucking him so at least he wouldn't have to go through temporary celibacy like he had been doing with Quinn. However, as with all his plans, the shit hit the fan and the plan blew up in his face.
The only real reason why this whole plan was even made was because of what Mercedes said to him. Now, although Mercedes usually isn't the most go-to girl for advice (according to a rumor that she fell for Kurt, the most flamboyant gay Puck had ever seen in his life) she actually was making sense when she told Puck to back off. At first he'd shoved the advice aside and convinced himself that Finn wouldn't even want to raise a kid and that Quinn didn't ever really love Finn. However, that delusion quickly disappeared once they were brought into Mr. Schuester's classroom together. It was then that Puck realized he had to take Mercedes's advice and back off from Quinn.
First of all, the execution of his plan got jumbled when Quinn had agreed to babysit Mrs. Schuester's sisters' kids. Not only did she agree, but she also decided that she wanted him to tag along. Puck had already mentioned that he hadn't gotten any to his friends and Santana seemed completely desperate to just give it up to him right on the spot. So, she was pretty pissed once he said that he couldn't see her that night because he was baby-sitting with Quinn.
How Santana got his phone number in the first place, he'll probably never really find out. However, when he was tied up in that chair with Quinn and facing those kids from hell he'd be lying if he said he didn't welcome that first, albeit bad, sext. Although he wanted to split from Quinn gradually, he somehow knew that he could never carry out with "breaking up" with her gradually because he'd just keep falling for her. So, in that split-second of an epiphany he sent back his first sext to Santana.
He'd never really planned for what he'd feel when Quinn found out about him and Santana sexting. He wasn't naive enough to think that she would never find out, but he never thought that he'd feel that much guilt when she did. So, he did what he does best and acted like an asshole. He gave her a clean-cut breakup because he knew she'd heal from a breakup where she thought he betrayed her for selfish reasons much faster than if she knew the truth.
Even though his plan had 'worked' he couldn't help but feel like his heart had been ripped out when he saw Quinn and Finn walking side-by-side, hand-in-hand out of school. As he drove home, however, he couldn't help but ask himself if five minutes of bad sexting with Santana was really worth a lifetime with Quinn and his kid.
Author's Note: My first-ever Glee fanfiction (on Thanksgiving nonetheless!) God, did Puck seem like a complete a*hole to anyone else on last night's episode of Glee? Oh well, when one acts like an a*hole then I somehow end up writing a story to make them seem like the good-guy with messed up plans. Hope you liked my trying to salvage the Puck/Quinn relationship. (By the way, does anyone know why there are so many Rachel/Puck shippers because I have no idea.