I know that the guy is into the manager but I can see why so many people assumed that he might be love rival with how he acted towards Sasaki and considering how jealous Yamada looked.
But I do hope they use the side couple to give us more progress while prolonging the manga through another couple to focus on and not just put Sasaki and Yamada/Tayama on the sidelines for them. I do think we will probably get a conclusion to the side couple by him confessing and maybe them getting together before we will get a relationship between MMC and FMC tho, because it pretty much always is like that
But I do hope they use the side couple to give us more progress while prolonging the manga through another couple to focus on and not just put Sasaki and Yamada/Tayama on the sidelines for them. I do think we will probably get a conclusion to the side couple by him confessing and maybe them getting together before we will get a relationship between MMC and FMC tho, because it pretty much always is like that