My friend is engaged and she had a crush on a guy and told me. Her crush is into me though and has been flirting with me. What should I do?

I feel crappy, I flirted back but I’m feeling so guilty. I don’t wanna jeopardize our friendship.
My friend is engaged and she had a crush on a guy and told me. Her crush is into me though and has been flirting with me. What should I do?
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