oh gosh ((hugs))
Take time to recuperate and get better.. don't expect instant miracles..
I was devastated when our doggie died too, a few years ago, time does heal and it'll get better.. (even though you might not think so right now..) I was against euthanasia, so we quarrelled about it at home, but at the end the doggie gave me a sorta reproachful look, so... I don't know?
The important thing is that you loved your cat and acted out of LOVE!!
Try to remember the good bits..
Do you have any friends locally you could go for a walk with or such? Any movies or books that could distract you? When Grandma died having books around helped a lot!! (such that I hadn't read yet!)
There are pet loss grief support forums online too, you know.. Some people get more affected by this than others, even if people around you don't seem to understand you, know that your sadness is valid, genuine and understandable... Maybe it will help you to talk with people also going through that, or who have gone through that..
Also try to stay away from gluten and too sweet stuff and see if it helps, it made my crying worse..
((hugs))