His real hygiene habits
Maybe all of this time together showed you that your partner only washes his hair once a week. Or that he washes it twice a day (so that’s why you’re always out of shampoo). Perhaps he claimed that he flosses twice a day and has no idea why he keeps getting cavities. But you barely saw him floss once a week throughout this. And after being present for most of his trips to the bathroom (not actually present but, close enough) you’ve learned that man does not wash his hands every time he uses the toilet. Gross! You don’t want to act like his mom, but you may need to talk to him about that.