How do I design games without it feeling like manipulation?

You've developed something powerful: you can feel what a player will feel before they do. That's the heart of great design, and it's also why you're uneasy, because the same skill that delights people could be used to hook and exploit them. That discomfort is your conscience keeping watch, and it's a good thing to have. The line between good design and manipulation isn't in the technique. It's in who it serves. Design that respects the player leaves them better off, entertained, challenged, satisfied, glad they spent the time. Manipulation leaves them drained and used, chasing something that was never really for them. Same tools, opposite intent. You already feel which side you're on, or you wouldn't be asking. Keep the question alive as your guide. For anything you design, ask whether the player would thank you if they saw exactly how it worked. If yes, you're serving them. If you'd rather they didn't look too closely, that's your answer. That honesty is what keeps your gift on the right side of the line.