The dupe of friendship, and the fool of love; have I not reason to hate and to despise myself? Indeed I do; and chiefly for not having hated and despised the world enough.

This quote means that the speaker has been foolish in love and has been fooled in the name of friendship. The speaker thinks it is their own fault for not hating or disliking the world enough. They feel that because they didn’t spend enough effort and energy on being cautious, they have ended up in a difficult situation.