DS (2.8) is obsessed with his friend. We see her socially and at a toddler group but they are in different pre school classes as she is a year older. He is struggling with going to nursery as he just wants to see her. In addition he talks about her 24/7. Anything you ask him he answers with her name. All his imaginary games involve her. When they are together he is happy to play with others too and for others to join their games but I'm worried because I think his obsession is starting to make him unhappy