How can one overcome the obsessions of weak personality, fear of failure, sexual frigidity, and impotence that plague the questioner's life?

These delusions and whispers are from Satan, and their cure lies in repelling them, avoiding thinking about them, and avoiding the causes that lead to them, such as solitude and excessive rumination. Occupy yourself with remembrance (dhikr), reading the Quran, and seeking refuge in Allah. You can also consult specialized doctors. Expecting failure contradicts having a good opinion of Allah, and you must take the means to success. Sexual frigidity is often not known to exist until after marriage, and it can be treated if found.