Is my girlfriend using me?

I have been dating my girlfriend for a little over two years now and everything has been great overall. I'm a college student that is about to finish my senior year of college and she is in the middle of obtaining her associates degree and my parents have warned me about my situation and for a while. Shes a great partner that supports me and she is a dependent woman that works full time as while I work part time till i finish my last two college semesters. Since the beginning our relationship, we have worked together and have had some great memories, but lately since she has been in school it seems like she has been asking me to help her alot with home work and other things. I wasn't really worried about my situation at first because we have a good connection and she doesn't ask me for money or anything. Our sex has also been on a big decline since i have been home for the summer for some reason, and when i politely talked with her about it and she said their was no problems. I know she is not cheating on me, but I am just wondering if she has been using me because she knows that I will soon have a strong career. I love her soo much and I feel that she loves me to but I just don't want to risk getting into a future marriage that is a yo-yo relationship. will someone please give a third opinion on my situation.. any type of advise would help!