Should I tell her how I feel, there is one big problem?

I developed feelings for a girl before I found out she has a boyfriend. She doesn’t talk much about him or bring him up when we are talking. Her and I flirt a lot back and forth and even playfully touch each other. I catch her checking me out all the time and staring at me whenever I’m not looking (she looks away when I catch her). She gets super jealous when I flirt with girls who are single.

She has no clue I like her because I treat her like any other girl at work. Should i tell her how I feel or hide it?
Should I tell her how I feel, there is one big problem?
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