looking my boy

I have too put him down today everyday for past month at vet diabetes cushings pancreatitis. Then became anemic. We did anyone  ultrasound and he has a mass inside that is bleeding . I am doing the whole self blame. Should  walked him more should've  not worked so many hrs. Replaying every imperfect thing I did just feels like looking my kids all over again and it feels like he'll  I don't want pity I'm so sad and angry I sit by his side and. Count down the hrs.I'm happy he won't suffer anymore but feeling selfish cause I don't want him too go he's my best friend