Is it still a crime if she ordered dessert?

No. She doesn't owe you anything, unless she agreed beforehand. You spoil your partner so that you can do something nice and so that they'll feel good, not because you want sex. Your partner is not a prostitute, and if you have no respect for her other than that, then you are a douche.
I don't understand why these people don't seem to understand the concept of boundaries and personal space. It is not your body. Unless she's seriously injuring herself, you have no right to invade anything that's hers.
Imagine if other people acted the same way to you. You have a bunch of friends over for your birthday and they all get you presents. One present is wonderful, and you thank the person who gave it to you. You think it ends there, but it doesn't. After the party he rapes you, because he believes you owe him for the present. You didn't think there were strings attached. You thought he gave it to you because he cared about you. But it was all a lie. Would you like that? Think about it.