How do i get over my dead cat?

i have had my cat since i was 3, and now im 16 and he just died. my family and i realized he was sick this morning, but we didn't know it would end up like this. the worst part of it is how we've been treating him the past few years. we moved into a new house about 5 years ago, and because we didnt want cat litter and stuff being tracked through the house, we made him and our other cat (who died a few weeks ago, but im over him now) live and stay in the basement. these weren't the greatest accomadations, and i actually hated them both for a long period of time because i was the one who had to clean up after them. but now, i feel incredibly guilty and angry at myself, because i didn't spend the time i had with my cat, and instead looked at spending time with him as an obligation. and now that he's gone, memories of when i was little are coming back. i remember i would always sleep with him at night because i felt he would keep the monsters away. i remember playing with him. i remember watching him wrestle with my other cat. but these memories are making me feel incredibly sad and guilty, and i want these feelings to be gone. please help