My kitten is a loner,what can i do?

ok well i foster kittens from the RSPCA and give them back when there big enough to get sold.We get them in litters of 2-8 but sometimes more.We have 3 gingers at the moment 7 weeks but very small for there age there is Prince Harry,Bruno Mars & Raffaello.Anyway Bruno and Rafaello always play together and have heaps of fun but Harry just sits there all alone and thinks he is a human he just sits there looking so sad or just sitting on your lap and harry depends on me SO MUCH when hes out and need to go to the toilet he will come to me and meow and i have to put him in the box.Rafaello was playing with string and Harry ran over to play (i thought thia was good) and harry tried to play but he couldn't so Rafaello gave him a look an walked away not he is such a loner and depends on me SO MUCH he is really cuddly but is a loner.What should i do?