I think this is a big error. She should have waited until he had just stuck it in then told him. His shocked face would have been even greater, and he'd be compelled to continue , whereas the way things are going now it looks like he's just going to run away. Then again, maybe she doesn't want to lose her virginity to him when all she really likes is the sense of naughtiness of seeing him guilty and she gets the ick when he's normal and happy.
Besides , is he really unable to get hard without being licked? His reaction to her boobs and several other times spent learing at their bodies suggests otherwise.
I'll miss this manga when it's over. The author has played it masterfully. I love these two sexy teen sluts with banging teenie bodies.