@Jezzballs2000
Oh sweetie...... I'm so, so, so sorry. 
I think when a cat is old and ailing and weak and frail - like 17 to 20 years old or more, and you have to get them put to sleep, you know it's the best thing for them. It's the kindest thing to do, you wave them goodbye - over the rainbow bridge - with a very heavy heart, and sadness in your soul, but knowing it's the best thing for them...
But for your lovely boy, who has been taken at just 10 years old, that's so devastating ...😢 That's just like, middle aged. That's like a human dying at 45! Just far too young. And for him to be tragically killed by getting hit by a car - that's very sad.
He's absolutely gorgeous! Look at his beautiful face. 
I do feel your heartbreak because we did lose one of our beautiful cats at just 7 years old. (Some years ago.) We never found out what happened to her. She went missing for two weeks - and then was found behind somebody's garage when they came home from holiday. Looks like she had been dead for a while, and it looked like she died the day that she went missing.
We were absolutely heartbroken. My two children were only primary school age at the time and they were devastated. We never found out what happened to her. We just assumed maybe a dog attacked her, or it might have been a massive rat or something.
I really don't know what to say to you, except you really have my sympathy. 
I'm really sorry that there's nothing I can say to make it better. I just know that time will heal ...
Thinking of you tonight, and your pain and sorrow... Take care. 💕