Help with a guy situation? Please answer!?

I like this guy who lives like a couple of hours (diff. state) away from me. He is visiting before summer. well, we like each other and he admitted it to me and asked I liked him. I said I did, but hes not only my friend. He's my sister's as well, who is a 1 grade apart from me (im older). We talk on the phone every day (my sister, the guy i like, and me). We are like talking, telling jokes, etc. but my sister tends to talk A LOT when we are talking on the phone. Sometimes she talks about like guys i used to like and says i did stuff i didnt do with my last bf (im 14 btw). And she like embarasses me sometimes, listing all the guys I liked and stuff. Sometimes she talks so much I think he likes her instead of me because she makes me seem mean or weird or stupid. It gets really annoying. I told her that she talks to much and she says that she cant help it. I tell her to stop embarassing me, she wont! Help please!! Will he eventually stop liking me because of her? Since she says this?