Oh Wow, I really know what you're going through.
I've been a foster carer for the RSPCA for over 10 years and taken on many many cats/kittens, dogs/puppies - even a horse! I'm such a sucker for the gorgeous little things, althought I now have a baby boy who is allergic so no more kitties
- Dogs still come and go. So so so many tragic stories follow these animals, it's absolutely heartbreaking. I had a kitten, that came to me after both of his front legs were broken by teenagers who thought it would be neat to throw him off a second story building to see if cats really do "land on their feet". When I think of the absolute fear that kitten must have endured while being tortured for god knows how long it just brings tears to my eyes. (Happy to report he made a full recovery, was the most adorably affectionate little ginger boy and has a forever home with a lovely couple as an only pet). But these stories are just the tip of the iceberg.
Do you have an association with any animal rescue group that could help with costs? Sometimes if you speak to Vet's they can offer discounts for animal welfare carers who use them for treatment on a regular basis?
Good luck, and yes - it's quite normal to cry when you find them homes...I always did, sometimes I was sad to see them go, sometimes it was because I was so happy to know what a great life they had install for them after what they'd been through..