I just want to say what a kind and considerate young man you sound. This is not your fault, even though you feel guilty. Your life is your choice and you can't let others rule it, even if they are family. It is still fresh now so your mum will look hurt for a bit, but it's not your fault. Just remind her that you love and appreciate her and everything she's done and that's never going to change. This is just the difficult part but it will pass.