I think its a hard time for your mum, illness sometimes does funny things to people, as would be expected.
I don't think your being completely selfish, but i am sure there is probably a reason for your mums behaviour. Have you tried talking to her and explaining how you feel, but in a calm way as im sure she is pretty fragile at the moment, or even talking to your dad about it?
Your friends probably dont mean to distance themselves from you, or appear as if they dont care. People just get caught up with their lives and what is going on in the present. Im sure they still care about you and want to know your okay.
As for your ex, sorry i cant help much there, you could just tell him how your feeling, if he throws it all back at you, atleast you have tried, there isnt much more you can do.