Should I be worried about my cat?

I brought a kitten home today he is 8 weeks old. I have another cat he is One. It wasn't working out because my cat hated him and was mad, and He ha lots of fleas so I brought him back. I am worried about leukemia transfer.. so u think I should worry about that? I mean, that kitten was here for maybe fours , and they didn't share food or drink, and possibly touched nose to nose. They sniffed each other through the crate he was in. The kitten pretty much slept and they weren't near each other. So my older cat is fine? right?