Did you get hurt really bad in an earlier relationship? If so maybe the shutting down as soon as you know you like him is to protect yourself from getting hurt again.
Zen

<font color=green>The snow falls on no two trees alike, and the forms it assumes are as various as those of the twigs and leaves which recieve it...so one divine spirit decends alike on all, but bears a peculiar fruit in each--Henry David Thoreau