Why are you making it so hard on yourself? If you want fwb only, then stick to it. Since you said yourself that you are starting to like her, it does not matter what signal she sends, you can end it and live a less complicated life. You should focus more on your studies and do not let this ruin your future. This agreement going into a relationship will be a burden waiting to happen and you are already seeing the tip of the iceberg. You have one shot at finishing your studies but if you get a job and a career after ,you have endless options. I can say this because when I was studying, no girls, no relationships, and I did well both in college and after.