Okay, I'll be honest, you've designed the game in a way that I can't actually make critique about the gameplay without opening myself up to "that's what she said" and "been there!" jokes. But I'm gonna try anyway.
Personally, I really dislike the gameplay because there's basically no feedback if you're actually doing the "right" thing and the upgrades feel like they barely do anything in terms of lengthening the gameplay. Like, I see a red "damage" meter pop up on occasion, but I see 0 connection to me doing anything differently, and no matter how many sensitivity upgrades I get it doesn't seem to get anymore consistent. The auto function actively hinders progress and gives you a bad grade? So what's the point then? I thought the point was to save your fingers from clicking, but apparently that isn't the intended use. "Drain control" is a complete and total mystery with no explanation on what it actually does. The "foreplay" stage doesn't make any sense and basically serves no purpose beyond wasting time. You'd think it have some kind of function as a pre-sex warm-up that makes the character easier to climax if you complete it correctly, but that doesn't seem to be the case.
I think the game has a cool concept, but when you're 10 upgrades in and it feels like nothing has changed, there's a major balancing problem at work here.