There was an attractive woman where I worked for three years. Despite being married I fell for her (she was unmarried). We spent alot of time, just the two of us and we had alot of fun. For her it may or may not have ended there, but I was obsessed. I never acted on my feelings and while I think she had them too (never really know for sure) she respected my marrige by at least not making a physical move. This was a little more than a two year ordeal. My wife eventually caught on and it was difficult for both of us.
The other woman and I had a little of a falling out and I took a better job a few states away, my wife was happy to get away from my crush and pushed hard for the move in our discussions, though she never brought this up in the process.
Neither me or the other woman tried to keep in touch when I left, she became involved with someone else and I wanted to save my marriage. This was three years ago. I think about her every now and again and maybe always will, but my obsession ended a long time ago. Distance and cutting contact off were effective.
At the time I was happy with this outside woman, but I also carried alot of guilt. Now I am probably happier, approaching 10 years married and have two young sons with my wife.
If you want to get over this crush cut her out. That worked for me. I also now know, as a married man, to avoid one on one time with attractive women.