Use Facebook and other social media and network the animal. Don't dump him at the shelter. The shelter is always a last resort.
Is the cat fixed? Or the females fixed? Much like dogs you can use a kennel to provide him with a safe area while he trys to adjust
If you keep them separated, you should do so in a way that lets them smell each other without seeing each other. After some time, you can let them be in the same room , although in separate kennel cages. Once they calm down (over a fair amount of time), you can gradually begin to introduce them to each other.
He just needs a little time to adjust. It's not always easy, but don't give up on him. He'll adjust.
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