How to cope with putting a fur baby down

My dog had another aggressive episode resulting in the absolute heartbreaking decision of putting him to sleep. I’m crying as I write this. He’s young so it makes it even harder. But he’s bitten one to may and is attacking my daughter and I. He’s been my baby since he was 6 months and he’s almost 9 years old now. I just would like some advice on how to cope with this.