He likes me, but I like his friend?

I realized that I like this guy named Ryan a few months ago when I asked a question to one of my friends about how you know if you like someone. She said that you get butterflies in your stomach, when you talk to him you get really nervous as if you were forced to do a speech in front of millions of people, you feel like you're floating on a bed of clouds, you think about him constantly, and smile when you do, even if you don't know it. All of that happens to me. He's a computer nerd, he's cute, and very funny! Anyways this guy named Austin liked my friend Sylvia whom refused to go out with him. I tried to get him to forget about her because he was really sad, almost depressed. After a few days he told me that he got over her and started to like someone else. It was me. He said he got to know me and thought I was cute, funny, honest, and all that stuff. I told him I didn't like him that way, but he refused to listen. A girl asked him out and he said yes. A day later she broke up with him. He said he liked her like how he liked me. He FINALLY stopped liking me in that way. He got all sad again so I tried making him feel better. He falls for me again! I've tried to talk him out of it, but won't listen! Yesterday was my birthday, he said that he was going to tell me something on Monday at school as my present. He wouldn't tell me what he was gonna say. Ryan is one of his best friends and I don't want him to know I like him because I don't want to ruin their friendship. I've been flirting with Ryan for a week or two now and I think he's starting to realize I like him, because he looks at me all the time (in a nice way) and comes up and talks to me a lot more than usual, and smiles and winks at me from time to time. What if Austin asks me out? We don't really talk in person anymore since he said that he likes me. What do I say? If I say no, what do you think his reaction will be? What if he gets sad again? Please help! I need advice!! Thank you. -Jamie