Is he happy the way he is? If he is comfortable with himself there is no need to worry. But if he is showing anxiety, or fear, or odd behavior, then this requires looking into. You might also consider that this might just be a phase.
I think its okay he wants to be with you ,he will make friends when he is ready to forcing him to may have the reverse effect. It would be good if you got him into some sporting activity, instead of the games inside ,have you a basket ball hoop thats a lot of fun,he may be shy and slow to get to know other childen , not everyone is gregarious take a step back dont try so hard and maybe he will make a friend and surprise you ...