When does nervousness become awkward or too much in a relationship or dating phase?

We all know that sweet feeling in your stomach. The one where you’re just completely love struck by somebody you’re seeing/speaking to and think things can go places. For some of us this manifests as being shy or nervous but in an endearing way.

My question is where is the line. When do you think nervousness or shyness is too much? When does it no longer become endearing? If ever.