My cat Graymalkin died recently. She was 17 years old, and went peacefully curled up in the sun in one of her favourite sunning spots.
From when she was a kitten she would snooze or just sit and chill on my lap whenever I was at my computer. She got me through uni and a bad breakup which had me running home to Christmas Island for a little while. If not for her I wouldn't have gone back to Perth and would have ended up living a completely different life. Her weight (what there was of it, she was a teeny tiny cat) and purring and soft fur got me through all the things that required focus and concentration while sitting still.
It's really hard concentrating without her there, and my chest hurts as I wait and then remember she's not going to jump up now.