What is the main conflict in About a Boy by Nick Hornby?

Will, who is responsibility free at thirty six and living off the proceeds of his father’s career at thirty six, is pretending to be the father of a two year old boy so he can date the women of a single parent’s support group without commitment. Marcus is a 12 year old boy in desperate need of a good friend and mentor as his life is unraveling both at school and at home with single mom Fiona.