Hello Neireid!
Yes it's very hard to lose your little friends, especially when you finally have to make the decision for them and after you've worked so hard to help them survive. I totally sympathize what you're going through now. I actually found a new friend fairly soon after I lost Hammy. I finally decided that the years of happiness that you garner through that relationship is worth the inevitable things you have to deal with at the end.
So for me, I'm happy that I got my new little friend. His name is Henry (I kept the name from the shelter). He was a problem cat and had to be returned from the previous adopters because he didn't get along with their child. Originally he was a skinny somewhat lighter version of Hammy, but he reminded me of him. I wanted to try and help him when it was probably the end of the line for him otherwise. After 2 years, he's mellowed greatly and has turned into a wonderful little cat and is my constant shadow.
I remember right after I lost Hammy, I was in the same mindset as you are.... "NEVER AGAIN!". That pain and energy lost as you go through that seems insurmountable. But it does get better, and I'm now glad I made the choice and adopted again.
I'm actually going through this whole thing again; my white cat is suffering from renal failure, so he's slowly dwindling away. I have daily sub-cutanious fluids I have to administer to help him manage. But we do what we have to do for our family and critters.
Even after all that, my advice to you is go out and find yourself another furry companion and enjoy the 98% of the time. Try and not think about what you KNOW will inevitably happen. Just reflect back on the joy you got from the rest of the 98%.