When I first began keeping fish about age 17, I thought a juvie clown loach was diseased. Whether or not it was, I pulled it out of my tank and killed it on a cutting board. I can still see his little eyeball looking at me like, HEY WTF! Afterwards I immediately felt sick to my stomach and it always stuck with me that I had other options to help it, and that that life was my responsibility. I don't name my fish, I don't talk to them, but I do become attached in that sense. I still feel bad about it and have always done the best I can to give my fish a happy life, because when they're happy, I am.
OP: There is nothing wrong with how you feel. You are doing your vest to help and that's all you can do.