How to be more patient?

I'm sorry if it makes me sound like a horrible person. But sometimes, I can't control my anger at my father who has Alzheimer's. I have OCD and sometimes when he pees in a bucket at night, or does something that mildly annoys me, it's so hard to keep my calm. Initially I patiently try to make him understand in easy words. But his comprehension is pretty much gone. I want to learn to better handle him. To be patient and not resent him. What should i do. It's getting so incredibly hard :(