Help I think I messed up really badly.?

The shelter should not have let you adopt this cat. It is miserable at your house. And your own cat is miserable, also. Some cats, just want to be loners. Cats are not pack animals, like dogs. So, a lot of people only have one cat, and that makes the cat very happy. It's a shame if you are going to make these two cats live together for a YEAR! Find the new cat a new home now, or take it back to the shelter.