Laura,
Have a Big Big Hug!!
You can and are dealing with this and are human. This is not easy as you have already discovered. You cannot expect to turn your emotions off and always be a pillar of strength. A good cry, believe it or not, will do wonders for you. My shoulder is always here if you need it. Your strength can only go so far and then have to be recharged. The care, love and support you are putting forth for your father are incredible. You are right that it is not all about you, but you have to take care of you to be there for him. You need rest, you need support, and you need to take moments to be emotional with him and away from him. Don't get discouraged you are a wonderful daughter and I'm sure your father would agree.
Stay strong Laura, and know all of us are here for you.
My thoughts and prayers are for you and your father.

Mike