I don't think she was ever using him in a deliberate sense. She is 16. What 16 year old has not been confused about relationships?
She has different feelings for Peeta and Gale and how would she be able to distinguish what is love for either of them? There are different types of love and I don't think a 16 year old would be able to sort that out in their heart or head.
She only fully understands her feelings in Mockingjay although I think there are some hints during Catching Fire to suggest to us that she is on love with Peeta. When you re-read the books you can see these hints much more clearly than from the first time reading.

