Can anyone help me in managing the stress caused by betrayal by a woman whom I loved and trusted?

I did things for her believing she would continue to be my close friend for ever. But she has started suddenly withdrawing from me. I don't mind that she is leaving me because if some one is not interested in me, it is better that they leave rather than getting stuck in a loveless relationship. But I hate myself for trusting for over three years that she would be my best friend for the rest of my life. This leaves me with a feeling that I have allowed myself to be cheated by her. (Idid some financial istance to her out of love fo rher.) I dont hate her because I have come across several such people in life. But I hate myself for not judging her properly before trusting her. I need advice.