Once the guy I like asks me out, I instantly lose interest?

I'm the same way.I like the feeling of having a crush and the anticipation of waiting to see when/if he'll ask me out but once he does its like wow its not all its cracked up to be:P I was dating this guy who I kinda liked but every time he would suggest he liked me it would push me away and I just wouldn't want to be around him but when he lost interest in me I started back liking him;PI guess we want what we can't have