What do you advise me, as I have been afflicted with the obsession of death, and I have come to believe in the superstition that a person feels the approach of their death 40 days beforehand, which has made me count the days as if I know the unseen?

You must turn away from superstitious thoughts that have no basis and occupy yourself with what is beneficial: reflecting on religious and worldly matters, accompanying righteous and pious people, and striving to draw closer to Allah through obligatory and supererogatory acts of worship. That is the greatest way to banish whispers and achieve a good life, along with frequently supplicating for these delusions to be removed. It is also advisable to consult the counseling department.