Kill the first lover

From Chibi Manga:
Is it possible to have a peaceful breakup with your first boyfriend? Yui’s first boyfriend, Agatsuma-kun said the worst breakup lines in middle school and transferred schools. That guy came back during spring of second year in high school, with coolness doubled and arrogance tripled!? Even worse, he kissed her in front of everyone, causing huge confusion!! Unlike before, the kind way he touches her causes her heart to race, but she definitely refused to let this return to the relationship they used to have!