Kourtney Kardashian and ex-boyfriend Scott Disick have been reunited for the sake of their son. The former lovers came together over the weekend to celebrate their eldest son, Mason’s 13th birthday. The event comes amid tensions between Kourtney and Scott after she married drummer Travis Barker. Members of the Kardashian family including Kim Kardashian, Kylie Jenner, Kendall Jenner and Kris …