How do I know if the girl I'm interested in has a crush on me?

I've been friends with girl for a very long time... All of our friends think we are in love but we aren't... But recently I've noticed myself having extra feelings for her... I think she feels the same too.. But sometimes I feel the opposite... So I'm looking for ways to find out if she is interested in me too..
(Yes asking her is not in the option. If you have a better idea.. please be free to share your opinion)
How do I know if the girl Im interested in has a crush on me?
How do I know if the girl I'm interested in has a crush on me?
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