I'm new to the forum, but will offer you some advice anyway.
The situation you describe is not uncommon due to the pit bull's
unique heritage as a fighting breed. Many pit bulls do not do well in
multidog households. Some can get along with other dogs, while others do
not. Many pit bulls become dog-aggressive as they mature.
The tendency for aggression towards other dogs is heightened between pit
bulls of the same sex. In general, pit bulls do best as only dogs in a
household or placed with a dog of the opposite sex.
Is this dog spayed? Spaying may help decrease some tension
between the dogs, however, you will also need to carefully supervise, and
most likely, keep them separate from each other; once pit bulls have fought
with each other or another dog, it is unlikely that they will get along
with each other ever again. Please read some important information about
breed characteristics here:
http://www.pbrc.net/breedinfo.html
http://www.pbrc.net/fightinfo.html
http://www.pbrc.net/faq.html
Many owners find that they can keep both dogs while maintaing a Crate and
Rotate routine. Please read here for information on how to safely separate
your dogs:
http://www.pbrc.net/rotate.html
If you really feel that you must find a home for this dog, please
read here for information about rehoming. The dog MUST be spayed/neutered
in order to be listed on our site. If you need help paying for the neuter you can apply with PBRC for assistance:
http://www.pbrc.net/fund/ap_neuter.html
http://www.pbrc.net/submission.html
http://www.pbrc.net/adoption/owners.html
http://www.pbrc.net/adoption/reality.html
http://www.pbrc.net/adoption/screening.html
Please keep in mind it takes, on average, 6 months to rehome a pitbull.