Sometimes after I make it clear that I am interested in a girl by a direct advance like asking someone out or confessing my feelings this mental change happens and it's harder for me to interact with them (I overthink things, get really nervous, freeze up and end up not saying anything sometimes). Before I made a move we were able to get along well and have natural, organic flowing conversations without overthinking or stressing even though I liked them.

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I first thought that it might have to do with them actually knowing now that I'm interested. But now I'm thinking it might have more to do with expectations and striving for a certain goal?

Either way, any advice on how to get over/avoid this negative mental change?