Thanks for everyone's replies, I'm so upset and can't stop replaying the scene over and over again. If he had been hit by a car and I wasn't there and was told later, I would be sad, but nothing like this :(
Without going into too much detail I watch him die right in front of me, full of blood and his head with in a bad way, an u image I will never forget :( my poor little guy.
We got him as a kitten from a rescue and I soon realised he wasn't a normal cat, he couldn't walk straight, fell over a lot and his head used to wobbly when he concentrates, the vet said he had wobbly cat syndrome and he prob shouldn't be allowed to go out, so I was going to raise him as a house cat. Fast forward a year and one day I watched him climb up the trampoline netting, along the fence, jumped down on the bins and the he went over the fence (he couldn't jump like a normal cat) obviously i tried to get him back in and moved the trampoline but he did it again and again, and used to wait at the back gate until I let him back in, over time he mastered how to jump back in, I even moved the trampoline to the middle of the garden so he couldn't climb out and he just sat there and cried all day until I put it back, he got the taste of freedom and didn't want to stay in all the time, neighbours kept their eyes on him and told me he was good with the road etc so I thought he was ok and going out made him happy :( he has had a ball this summer.
My partner thinks he was spooked by a dog, who was getting walked and was going past the place he darted from, we have dogs too so I'm not sure y he got scared :( I can think of a million reasons why it could of couldn't of happened but it won't change the fact that it did and he has now gone and I don't have my wobbly like guy anymore :(
I am getting him cremated and keeping him at home (it's what my children have decided too)
Me and my partner had a very hard day yesterday, we have since talked and I have told him it's not his fault and I'm not blaming him, I would normally ask for some space but I thought I needed to be with him and I think I made the right choice, we will be ok but it's going to be hard.
For anyone that asked we have been together for nearly a year, dating for dating for 4 of those months at the start, kids have met him and like him, and I have met his.
My apologies for the title, my head was not im a great place when I wrote this thread.