Need some serious help.?

I went through this same thing. I got my first cat as a kitten, then a year and a half later I brought home a kitten. At first, the cat absolutely hated the kitten, he would hiss and growl and seem like he was going to attack the kitten. We talked to the vet and he said it was just the cat being territorial and that it wasn't anything to worry about. Until the kitten got big enough to defend himself, we would keep him in the bathroom while we left the house- separated from the older cat. Now, they love each other. Of course, they'll fight sometimes- but that is normal. It shouldn't be anything serious once they can both defend themselves. But until then, supervise them when they are together, for at least the first few months.