It hurts, killing something you love. I mean *actually* doing it yourself. Not necessarily more than arranging for someone else to do it, sitting there while someone else presses on the plunger. In a way, that's harder. Because not only do you have to admit that everything is out of your control beforehand, but then you have to give up that last little bit. Give someone else that last, final authority.
But to physically do it yourself? That takes something different. Because after you give up everything, every last hope and wish, you have to do the unthinkable. You have to set up whatever is involved in the method you choose. That's after doing research, of course, to find the best, most humane method. And after you set everything up, you have to gather him up, which in and of itself may be difficult, if he's a fighter and uncooperative. You have to gather him up and say that last goodbye. Maybe try to explain why it is you're doing what you're doing. Maybe explain why you waited so long to take this necessary step. Maybe pray for that sign that never comes, that you made a mistake and everything is going to be ok after all.
And once you've done these things, these terribe, horrible, excruciating things, you have to do that last thing. That thing which will take him away from you forever.
That last, final motion is the hardest thing you will ever do. Because you know, as he will and can never know, exactly what it means. What you are doing and why. Taking his last decision away from him, his last feeling, his last everything. And he is gone.
And now his tanks sit in silent reproach on the bookshelves where they still remain, half full. Half full because in his final months, he was too weak to swim to the surface for breath easily, so you lowered the height of the water in order to make the journey shorter and easier. And it was what he needed. The tank on the right, which he never went back into, with sand on the bottom because you thought that might be gentler than pebbles on his ragged, tattered fins that had seen so much time for one of his kind, and survived disease you were sure would kill him. But he was a fighter. And you can't yet bring yourself to clean them out, empty them, because it will be the last thing you do for him. And you've already done so much, so many painful things, and you're not sure you can bear one more.
And you feel silly, feeling so much, so strongly, for one who was with you for such a short period of time. Who most people wouldn't think twice about losing, or if they did it wouldn't hurt them this way. You feel, somehow, like you failed again. Though you know with every bit of reason available to you that you didn't, you still feel like you did.
It never gets easier. And it shouldn't.