Did my cat catch ringworm from the vet and can I hold them responsible?

I'm a college student and I took in a half-starved kitten I found in my neighborhood about 4 months ago. He's probably about 6 months old now and hasn't been outside since I nursed him back to health. I saved up money to take him to the local cat shelter to get neutered a week ago this Thursday. Tonight (wednesday night) I noticed a patch of ringworm in his groin area. I know exactly what it is because I've had cats before who've had it, and I've had it myself. I know it was not there a week ago when I took him in because I inspected his incision (I've heard horror stories about the shelter). He and my other cat haven't been out of my house since I got him 4 months ago. Could he have caught it at the shelter, and can I hold them responsible? I don't really have the money to treat him right now, but I don't want my other cat to get it! Also, what can I do to keep from catching this??? I have scarring from the last time I caught it, and I don't want to go through it again! I'm terrified!