Martin, please accept my condolences on the loss of your dear Mum. Many people on this Forum talk about their feelings of guilt-and many tell them that they have nothing to feel guilty for. Please try not to dwell on not being by your Mum's side for her last two days-try to think of the days that you were there. Better that you showed your love (as you did) through the years that she was ill and able to respond to you.
Yes, you are in a dark place, and for that I'm truly sorry, but your Mum's suffering is over; she is reunited with your Dad.She will always be a part of your life -she helped make you the caring Son that you are.