Ohhh this makes a lot of sense now, dating a girl and then dating her best friend is a really dick move... this is kind of exagerated but a dick move nontheless. So the reason he didn't ask Tomo out before was because she is his ex's bff hahahahaha i can't get mad at him, at least the guy has some sense of honor.
Hey, at least Jun had good intentions, it's not like Misuzu has been making things simpler anyways! Well, I guess things between these two are clear now at least? ^^;