What am I supposed to do?

Honestly you do not sound the slightest bit selfish at all. Your parents should be ashamed of themselves putting all that pressure on a kid. Your mother ped her responsibilities as a wife onto a child. Your first sentence, I have always been a parent to my dad.....Honey, that is just not how it was supposed to work. You need to live for yourself, your dad needs to know that your are wasting your life because he might be upset. It is not your job in life to make things okay for your dad, he is supposed to make them okay for you. I am so very sorry for your situation, but you do not deserve to feel one single inkling of guilt, you have already given too much.