Should I forgive my Ex-lover/Close Friend or forget she exists??

Okay here's the situation, I became friends with a co-worker at the end of last year. We became really good friends really quick. And a month into our friendship, she told me she like me as more than a friend. To make a long story short, we began a sexual relationship. This went on for about 4/5 months. From the beginning the understanding was we would be Friends with benefits but I began to have feelings for her. Now she was honest in that she said she didn't want to be in a relationship at that time so when I realize I Loved her and wanted more I told we should stop fooling around. When I told her this, she didn't asked for an explanation or anything, she simply said okay and that was that.
Well within the next month, she began dating a friend of hers and they have been together for the last 5 months. We are no longer friends which is very sad because we still work together. When I asked her why wasn't I good enough, she said the age difference was too much( I'm 33 and she's 24) and that she wasn't ready to be serious at that time. But she had a boyfriend a month later???
She has repeated that she cares about me but just wanted to be with a guy her age. She has made multiple attempts to restart our friendship but it still bothers me how she handled everything......I feel played.

My questions are
1) Should I forgive her and if so, should we not try to be friends again?
2) Am I crazy for still being hurt after 5 months??
3) Is she a selfish woman or just immature?