I do believe that Eternum and the school life stuff is all one game. But from the POV of those in the story who think otherwise, I wouldn't put too much stock in sex in the game. It's like how in .hack//GU where people got depraved and loved killing in the game so much that they formed guilds just to murder newbies and troll people. Now imagine a group of losers IRL get into Eternum and become god tier in the game and everyone respects them for playing the game so well. And they bang whores all day long when they're not in raids. In their mind they pat themselves on the back for all the sex and fame they get but it's not real. It's just you playing a sim.
Unless there's some big reveal that playing Eternum is just teleporting your real body to a real world somewhere in space, it's all fake. So no matter how much fame or sex you have, IRL you're still just some jackass. Sure they say you have to work out to become strong in the game. But that's not how magic works. So if you stick to just mage servers and use magic and never work out you don't even have to work that hard for that.
The main problem with Eternum is what everyone is glossing over in the game. For all the glitz and glamor and depraved sex and war, none of it will fill the voids in their lives. For every Lex Luthor wanna-be trying to rule Eternum, that's still not the world. You're not taking over the world. It's a game. For everyone Isekai-hero-wanna-be, being the strongest in the game still means someone could shoot your real body as you sleep in your bed. None of it matters.
It's smarter to stop Eternum and the people who made it than play around in it and become part of the problem. And it saddens me that even the heroes have drank the Kool-Aid on that front. None of them care about helping people or the very real problems in the game and the society it's ruining. They care about sex, money, and winning. Maybe the whole point of the game is to teach people to stop being apathetic or selfish. The actual game, not the game in lore.