The actor, who moved to Los Angeles in 1993 along with his identical twin brother Jason, says that his rise to fame – he played Griffin Holbrook on the hit series Party of Five and Chandler Hampton on 7th Heaven – lead to a dangerous tendency to abuse drugs.
"I was treated like royalty," says London, 37. "It was hard for my brain to accept."
London wed actress Melissa Cunningham in September 2006, and the couple welcomed their son Lyrik, now 3, soon thereafter. But he says that prescription pill abuse contributed to the demise of his marriage and career – and jeopardized his relationship with his son.
"There were times I didn't care if I died," he says. "I felt like I was losing everything."
Currently going through a divorce and facing significant financial woes, London went to a rehabilitation center in September 2009 to face his drug abuse – and to prove that he can be a good father to his son, with whom he currently has twice-weekly visitation.
"I'm learning it's much easier to deal with life with a clear head," he says. "There are so many things I wish I could have done differently."
For more about London's battle with prescription pill addiction and his struggle to be a full-time dad again, pick up this week's issue of PEOPLE, on newsstands now