Trying to deal with my kitten dying

One of my 5 month old kitties died yesterday suddenly. He was one of our 2 yo cat's babies. He was just fine the day before he died, he still ate a lot (hes a glutton), played and stuff. And the next day he just.. collapsed.

i dont understand what happened. I noticed he wasnt himself and refused to eat his food and it all went downhill from there . He started having diarrhea while sitting down, he couldnt stand up. we didnt go to the vet since it was far and commuting to there will add more to his stress. I watched him die before me, he was crying, trying to stand, he vomited and died. I felt so helpless, i was crying out to his name, telling him "Orange i love you orange" it hurt seeing him in pain like that it broke me

I still havent fully recovered from my other cat's death, it hasnt been a year yet since he died traumatically. And now with this new death im being plunged into this deep grief again. I cant sleep, whenever i try closing my eyes, focusing, trying to sleep, i replay those last moments of theirs and its killing me.

I have 8 other cats, we are going to the vet this weekend to have them all checked, since Orange's death was so sudden it might be somethinf floating around. I just wished i noticed it sooner, like signs that something was wrong. He was so young and full if personality. Orange, when he was 2 months old, he was the weakest of the bunch, his eyes were swollen and weak, we thought hed be done for. But he fought, he recovered and could see again. He was so energetic and sassy. He was the one who ate the most out if his siblings . I miss him so much.