It's heart wrenching isn't it? Seeing your parents struggle with an illness eating away at that image you had of him from the earliest days of your life. He taught you to throw a ball. He always told you you're his princess. No matter what you cooked it was the most delicious of delicacies. He was always there for you when you needed a shoulder to cry on. He was always there to cheer you on. Now it is your turn to care for him. But it's hard to reverse the role of father and child. He's not such a good listener. Maybe if you had been stricter with his diet and exercise, he wouldn't have had another heart attack. Maybe if you didn't have to work so hard you could've spent more time with him so he would've been happier. Maybe if you were in there more frequently you could've made sure he always took his medications. You're in charge of caring for him. It must've been something you did.
As carers, it can be so easy to fall into an endless cycle of guilt and blame. But that does no one any good, and saps your strength, what little of it you have remaining after all that needs to be done. It makes the one you're caring for yet more depressed, because no matter how hard they try they can't convince you that it's not your fault. So now instead of caring for themselves, they're trying to care for you. All the guilt does is give you something to rail at when there are no answers. It makes you miserable and distracted when you should be enjoying each other's company, and the successes and joys of life.
Your loved ones are not their ailments. They are your family who love you, whom you love. They are their hopes and dreams, their life experiences, their joys. If you can look past their challenges, then others may be able to, too.
It's not you. Sometimes things just happen. Forgive yourself and accept life at face value, And perhaps you will give them an example of how to live life to the fullest, of how to turn their challenges to advantages.