In love with a straight girl!?

So I'm 15 and bi and and I've know this girl for about three years and I've liked her ever since i first saw her, although we only started really talking this year. She is literally all i think about. I care about her so much and I want her to be happy. I just can't get her out of my head! And we had a sleep over last night and played truth or dare. She asked me what my biggest secret was and I finally told her I was bi. She seemed cool with it, i think although now she hasnt really responded to my texts. She said she thinks shes straight, and was almost positive that she likes guys and thats it. I don't really know what to do, It's torture being around her but thats all i wanna do. I don't know if theres any hope, there probably isnt, and I don't know if she knows that i like her. I havent told her but she always catches me looking and then i blush and look away. And i've also made her gifts and stuff. I just don't know what to do!?