GF Cheated. Left me. How to move on?

All. My GF left me for someone else. She told me that she had cheated on me with someone else (a different person than who she left me for).. She said it was once but looking back in the weeks before she left me she started working "late". Its eating away at me that i let myself be treated like a fool and that she cheated on me. Also, morefool me, i still love her. How do i get over the betrayal and put her behind me. Im completely devestated. Any advice would be appreciated.