My girlfriend doesn't want sex. In the 4 years we have been together we have made love about 9 times. She has two boys aged 10 & 12 and she works part time and we don't live together. I help her out with stuff like buying her a bike so that she can join her boys, a new TV, a new cooker, plus I took a loan out to buy her a car. She says that she only has sex with me like it's payback for what I do for her. Am I being used?