Introducing two cats?

[NessaLovee]

We've had our cat Scratch since september, he's nearly a year old now. He's nuetered and goes outside often. We got a new cat today Stork, who is still a small kitten, a male, and has yet to be nuetered because he's to young. Today we made the mistake of letting them see eachother and although Stork was fine, Scratch hissed and isolated himself from the family. He went outside and hasn't came in yet, which is okay because he does spend nights out sometimes, but he comes and goes and eats and has a litter box inside. I feel horrible. What should we do? I don't want Scratch to feel like he's been replaced and kicked out of his house. He won't come in when we call him, even though I hear his bell! Suggestions? Please? Thanks so much!