I offered to take my girlfriend out to dinner but when she asked about dessert I told her I didn't want to pay for it
I bet she was disappointed. What made you not want to pay for dessert?
Cause I don't like desserts and I didn't want to spend too much money at the restaurant.
The person who extended the invitation should be prepared to pay for the entire meal. If you can't pay for the entire bill, you should not ask someone out.
I only expected to pay for her dinner, she can spend her own money if she wants dessert.
Most people consider dessert to be part of the meal on a date. You most likely hurt her feelings by refusing her request for dessert. She may be reluctant to go out with you in the future.