How do I get over the frustration of losing a friend who turned out to be fake?

My former best friend decided to ignore me for no reason. It all started when I began dating my fiance. At first, she pretended to be happy for me. Since she was unlucky in love, I never rubbed my happiness in her face and I made sure we still hung out and she didn't feel left out. The happier I was in my relationship, the less I heard from her. In the past, she had similar fallouts with all her friends and I was the only one left. I know this means she was never my friend but it saddens me that I was fooled by someone who never cared about me. I am now focusing on my real friends. How can I get over the sadness and frustration quickly?