I friendzoned her, but now I like her. How do I get over my feelings for regrets?

Three months ago I friendzoned this girl because people thought we were dating. I didn't do it purposely, I never thought she was interested in me so I never thought of her that way (maybe I did once or twice, but I didn't bother cause I thought it is better if we stayed friends). I did it because I thought it is better if we cleared that situation up. Anyway stupid me back in there couldn't see her signs, but now analysing them makes sense. Three weeks later she asked me if I wanna see her boyfriend, I thought she was joking so I told her alright but then she sent me a picture of her kissing food.

Fast forward three months, she told me about her boyfriend. She told me she has been seeing him since three months. So I was joking with her friend recently, and told her how big of coincidence for her to start seeing someone right after what happened between us. She told me she used to like you, but you didn't reciprocate the feelings. Now I can't the idea out of my mind, and it is really bothering me. I mean that girl was just great.
I friendzoned her, but now I like her. How do I get over my feelings for regrets?
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