I'm in serious need of advice and help.

Half a year ago my cat was fine. He was beautiful, healthy, talkative,
and loved to play and to be held.
Now he's always hungry and vomits up all the food he eats.
He constantly wants water. Not just any water, though, he wasn't fresh
water. If it's been sitting out for more than an hour he'll want
fresh.

He also doesn't like for other people to hold him- Only me.

He doesn't have worms.

We don't know what's wrong with him..
He's lost so much weight.
He used to weigh well over 10 pounds.. and now he's probably 6 pounds.
My cat is my best friend and if he died I'd probably never get over
it.

Please help me.