From his perspective he tried, only to find out that the girl he likes is actively trying to avoid him and her presumed boyfriend views him as a stalker. When you have zero confidence, these kinds of things make you convinced that no matter how hard you try, failure is the only possible outcome, so it's better to give up. Having said that, I agree with you @Starbright that the author made him too quick to dismiss people like Yuri and Hamin while putting his complete trust in Seo.Its to late for joonwoo to escape now hes already in the crazy bitch trap. Honestly with taeyang not bothering him anymore he should of just attempted having a normal school life and making friends and girlfriends the regular way.