@Vverg
I don't care about multiple partners thing. As you get older, you notice that PRETTY MUCH EVERYONE keeps saying they dated multiple people. Oh. . . . . okay, they virgins when they dated every single one. . . . . yeah sure bub.
That ain't the issue. The casual sex part however destroys suspension of disbelief because of how risky the reality is. Meguro would risked multiple Stds, probably botched birth control since teenagers mess up, risked pregnancy, as well as the fact she was being treated as an object. Oh and the pill is infamous for wrecking with hormones and can risk her health and making sex unpleasant which is awful, and since her old boyfriends were jerks, they probably weren't particularly nice or gentle, adding layers of ick to this.
And we get no explanation explaining WHY she took such big risks or accepted being treated as such. The explanation that she LIKED SEX or was an insecure girl would have worked WAY BETTER than, oh they were my boyfriend, then we immediately had sex. With her personality, I FIND IT REALLY REALLY hard to believe this would happen in real life would have ended up this way unless she actually a nymphomaniac. Which she ain't in the manga, YOU SEE WHAT I'M GETTING AT!