Getting over a crush

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Please help me get over a crush.
I've had feelings for her for a while, we went together for a coffee a couple of times at the start of the year, chatted a bit but I noticed that she was usually pretty formal with me and spoke like she didn't see me as a man, and never initiated contact either. So I put two and two together, realized it wasn't gonna happen and stepped back.
Now last month I found out that she and one of my mates started dating, with her asking him out, and everything came rushing back, I felt really upset about the situation for a while and angry at myself.

Now I've been keeping myself busy, went back to the gym, keep telling myself that I wasn't in the running anyway, became more productive, chatted a bit with other girls, deleted her number and minimized contact with the both of them as much as I can etc. but I still find that throughout the day I'll just start thinking about her and feel sad about the whole situation, obsessing over various retarded "what-if" scenarios. I try to correct my thoughts quickly but they just end up coming back.

Is there any surefire ways or psychological tricks I can use to get over her quicker?