Am I in love or is it only in my mind?

Hello. I am a boy, I am 26 years old, I have been working in a company for about 4 years and here I have a colleague with whom I think I have fallen in love. We have been friends for about 3 years (she came a year later than me), initially we only talked about work-related things, but we slowly started to talk about more personal things as well. She broke up with her boyfriend last year, but I didn't realize it and I didn't do anything to be with her, even though she gave me a sign and she was the one who approached me the most. Only now I realized that I am in love or really like her, also even when I am single at home, she is in my mind. Actually I don't know what it is either, but I like her, I like everything about her and we are also very good friends. What do you think it is, am I in love or is it just something in my mind? Also, how should I go about it, should I tell and propose her, and how exactly should I tell her?

Am I in love or is it only in my mind?
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