Salaam Paul
I do not know if this is a new thread or not, so I shall treat it as a new one and offer my apologies if it an old thread.
I am so sorry for your loss.
Muslims have a basic duty to visit the sick (not just family and friends), we must comfort one another in times of sickness. We pray with the sick person and read the Quran to them.
We believe life is a test and how we do in that test determines our life after death. Death is the return of the soul to the Creator. At the moment of death we know our destiny (heaven or hell).
We believe that death is like sleeping, complete with dreaming. The person waits for the Day of Judgement but the wait seems like one nights sleep to the person - though it may be centuries in our terms. Each death is by the Will of G-d, so we should accept death when it happens.
After a person has died we are encouraged to perform acts of charity, go on pilgrimage, fast and pray for the dead person. We also must look after the family of the deceased, make them food, look after children, etc - this gives them time to grieve.
It is natural for us to consider what we could have done differently but we cannot change the Will of G-d, we die when He decides. The dead person must be remembered and prayed for. However, once a person has died we must concentrate on our own test, on our own struggle to attain a place in Heaven. This can be achived by rememberence of G-d and good deeds. It may help you if you perform good deeds on behalf of the deceased.
I hope your pain eases soon.
Salaam
Sally