I'm so sorry for your loss, our pets are very much part of our family and it is often their unconditional love that helps us through the bad stuff in life. They are the welcome home cuddle, the one person you can pour all your sadness and fears out to without the worry of having to remain strong for others. You gave Teddy a lovely home, with lots of love and it is very clear that he has wanted for nothing. He had a very good life and you need to feel proud of yourself for looking after him and more importantly making the most selfless decision you can possibly make - you put him first and allowed him to have a pain free passing. That really is the ultimate gift you could give him, a thank you for all the love he gave to you. It takes a lot of courage and love to do that.
You now need to allow yourself time to grieve, as you would for a human friend. You don't get over this sort of thing in a few days, it takes months. Even more so when you have such a lot to deal with on top of that and it sounds like you are normally the one that has to be strong for everyone else. You can only take so much of that before depression sets in, all the goodness gets sucked out of your life and you just don't want to face dealing with any more. You are scared of what the next knock will be. If that is how you are feeling now and only you know that, then please, I urge you, go and talk to a doctor. There is no stigma involved in needing some help and it can be the turning point for a happier future. When you have so much sadness in your life it really does cause a chemical imbalance and there for the grace of God goes
any one of us. It needs a kick start to get it back to the right levels again.
I'd also say that when the time feels right you should consider getting another cat - NOT to replace Teddy, you'll never be able to do that. He was a one off. But our hearts have the capacity to give a lot of love and even if you don't get a kitten, then there are older cats in need of loving homes. Special people like you can given them a future.