I m sorry for your loss.
Having read your post, I have to say that I see your relationship with your late mother as a rather typical one. You said you have no friends outside work, and you don’t really seem to have friends inside your work either.
This is a typical Mummy and Son relationship where you have revolved your life entirely around your mother. A very bad idea.
Sympathy is all very well, and I do sympathise. I have lost my mum too, and my dad, not to mention parents and many friends. Most of us have. The difference is, we see it as a normal part of life and we get over it.
I am being hard here, but sympathy only goes so far, and I intend to tell you what I think. You have two choices here.
1st choice - You pick yourself up and make an enjoyable life for yourself (perhaps cultivate some friendships in or outside work). Maybe join a club, take up sport, or collect stamps! You become your own man! Whatever floats your boat.
2nd choice - you remain a typical mother’s boy for the rest of your life, no friends and only yourself to think about. You mope about with no plans, nothing to look forward to and little to talk about. Your colleagues probably still won’t speak much because you do nothing that you could all chat about. What are they supposed to say?
Come on. Pick yourself up. Re-invent yourself. Be the man your mother probably secretly wanted you to be. Make her proud!