Good for you! My Dad did the same (donated kidney to a stranger) about 5 years ago, and still feels very happy with the decision.
It was hard for me, because there's a non-zero chance that I'm going to lose a couple of years with my Dad because of this. I'm glad he did it though, because someone else's Dad might get to live because of it.
I assume you're undergoing counseling before the operation. If you decide you don't want to go through with it that's totally fine - the fact that you're considering it at all is amazing.
It was hard for me, because there's a non-zero chance that I'm going to lose a couple of years with my Dad because of this. I'm glad he did it though, because someone else's Dad might get to live because of it.
I assume you're undergoing counseling before the operation. If you decide you don't want to go through with it that's totally fine - the fact that you're considering it at all is amazing.