The unfamiliar jealousy that the news has awoken in Yuusuke has spurred him on to making his own plans. He's going to try to become popular, and get a girlfriend, before Misao gets married in the spring!
This description sounds extremely confusing. Makes it sound to me like the whole reason behind his actions is completely pointless. I can't tell if it's for self satisfaction, to try to cause some kind of jealousy, or whatever. I dunno, just feels like the author just had some random idea and just put it out there.