The “cat expert” is full of baloney. Don’t give Clint up. He will be just fine with you. But, if you’re worried about it, adopt another kitten. Even better, also adopt a slightly older (1-2 years) cat that can teach the youngsters all the cat ropes. Then you will be well on your way to being the neighborhood crazy cat lady! (just kidding)
Seriously, though, don’t pay any attention to the “cat expert”. You’re hooked on Clint and the only way you can guarantee he’s well cared for is to keep him. I’ve had over a dozen cats over the years (not all at once) and I had never heard of single kitten syndrome. All of my cats were either strays or abandoned kittens. Two of them were single kittens, and they both turned out fine.