I really like this guy but my twin is getting in the way and I think that it's to late?

So I like this guy. a lot. I already feel that he is to good for me and my twin sister made it worse. Ok so I'm in cross country and we run during the summer and that's where I met him. (I'm a sopre and he's a freshmen) I liked him right away. I told my sister that because she is the biggest flirt ever and I didn't want her to take him. She agreed to stay away but on Thursday when we went running things were going great. Then when we finished him and my sister had a rock throwing war with theses little rocks they found on the ground. I looked stupid when I tried to join in. Then she told him that he has the most beautiful eyes. Then we decided to climb up this mountain thing and he gave her a piggy back ride!!!!!!! I almost started crying. When we got to the top they started throwing rocks at each other again and then had a pushing war. When we started headed back down he stayed at the top for a while with my twin and they talked. I couldn't take it anymore. I just walked fast down the mountain and couldn't help but start crying. She agreed to "stay away and never talk to him again" but I think it's to late. It seemed pretty obvious that he liked her and I was wondering if it is too late for him to turn to me? What should I do!!!? I don't see him again until Monday.