My cat killed my gerbil

I've always wanted a cat since I was a little kid but my parents hate them

4 years ago I moved out of the country to study under my parents sponsorship. Took me 4 years to convince them to get a pet and they finally agreed under the condition that's it's not a cat because they wouldn't bear a cat for the few times they visit me

So I got 2 little gerbils and God knows how I loved them. I spent so much money to get them the best enclosure possible, I crafted a top platfoem for the enclosure. I Would prepare them food by myself by choosing the types of seeds, etc...

But no matter how I loved them they never fulfilled my needs... deep down I wanted a cat and gerbils aren't that social or cuddly. As I mentionned I'm alone on a foreign country, I don't have a lot of friends here and I never get out.

I've ended up adopting a kitty, and being aware that gerbils and cats aren't compatible, I've made some researches to protect the gerbils. I've improved the enclosure and try to work things up for the gerbils to be safe.

For a month it worked, just got the cat spying on them and watching them like TV

Unfortunately, today I woke up to

TRIGGER WARNING, GORE

One of my gerbils limbs and tail spread on the ground, blood everywhere. A butchery

I couldn't find the anything else from her

I went to inspect the enclosure and I can't figure out how she managed to escape, everything is locked up and still cat proof except for a part of the wood that has been chewed but this part couldn't be chewed from the inside of the enclosure which still raise the question. How did she got out

I feel very guilty, I feel stupid for trying to keep such incompatible animals together and I hate myself for that

I don't know what to do, I should rehome my remaining gerbil for sure and it's already difficult for her because she lost her pair but I don't know how I'd live with the guilt of being responsible for such a small creature and I don't know if I'd ever forgive my cat. I know it's not her fault, she's a kitty designed to hunt and I didn't scream at her or showed her sign I was mad but deep down I don't feel like being lovely to her right now, I'm mourning my little Coco

RIP my Coco, I hope that you didn't suffer as much as I'd imagine, and I hope I was able to give you the best life possible while you were with me

TL;DR; I've adopted a cat and gerbils and my cat killed one of my my gerbil