When I meet a guy, I get excited too quickly...?

Ok, here's the story. I'm a very reserved person, like that girl that doesn't speak unless someone talks to her. I am not shy, just reserved. I have a very hard time meeting people and making friends (but I DO have friends) because I'm not really much of a talker and I hate making conversation. I don't really have any friends that are guys for reasons that are unknown to me. And I'm 15, and I've never had a boyfriend, so when I do meet a guy who is interested in becoming friends with me, I get really excited and I start CRUSHING on him. I believe it is because I have very low self-esteem. I am very consciously aware that this kind of thing happens EVERY single time I meet a guy, it's just I cannot control it. Based on my personal experience, when this kind of thing happens, I usually DRIVE AWAY the guy, and he becomes afraid of me and starts to think I am a freak because I like him so soon. How can I get my unconscious self to take it slow?