His mouth is poison. She can taste something bitter on his lips. She can feel it, burning her skin, warning her. She knows that if this continues, he will enter her system and take over every part of her, and she will be helpless to it.
His mouth is wine. It is sweet and strong. When he kisses her, she sees the world through new eyes. Everything becomes fuzzy, and she can't remember any of the reasons she wants this to stop. The more she gets, the more she wants.
That's how it always is with him - a constant battle between poison and wine.