My condolences, it's always tough when someone close to you goes away permanently.
I remember how surreal it feels when you have to go through life without them even though they have been with you forever.
I agree with Drayker, time helps so much with coping; another thing I have to say is that you should try not to bottle it up when you have the chance, or try to distance yourself from your emotions during this time.
Sharing past memories of my loved one helped me a lot. Maybe you could try that too?
Just have a little chat with your Dad after everything is over, how your Mom was like when she was younger, how she met and things like that.
Please do not feel bad or inadequate about yourself because of regrets.
Also, be sure to smile after this storm because your Mom would've wanted you to be happy