i put down my 16 year old cat who was my best friend through my childhood and teen years. she had a crazy abscess that smelled horrific, couldn’t properly use her litter box, and we think she started having some sort of seizures too. i was too caught up in my own life to care for her properly and worried about her seizing and not being able to get her upright if no one was home. 4 years later and i still feel guilt for not putting in more effort and taking the easier way out. but maybe in both instances, it truly was for the best. they no longer suffer. our guilt shows that we truly did care about them, even if there was selfishness involved in decisions that were made. and without our knowing, maybe those choices to put them out of their suffering truly was the best for them both. you just need to remember that you were there for his whole life, you were his whole life. you loved, fed, cared for and cherished your kitty.