My Sophie has issues with most other females, and ALL puppies. Hates them. Buster does okay with most dogs, but hasn't liked either of the male pit mixes that I've fostered. Weird. It's not unusual, though. Fred's protecting his pack. You may need to keep the little guy in a crate until you find him a home, and keep the two boys separate. I'm glad you took him in, though. He needed you.