Matthew is opening up about the disease that consumed him for decades in an upcoming ABC special with Diane Sawyer. He's on a mission to help others who have self-isolated, because he's a firm believer there's no way out unless you have a support system. He says, "Alone, you lose to the disease."

The "Friends" star has been through a lot ... 6,000 AA meetings, 15 stints at rehab facilities. He's doing ok now and feeling good, and he credits people around him for keeping him on the straight and narrow. He singles out Jennifer Aniston for her assistance during the show and after.

Matthew's been in TV shows and movies since "Friends," but it's clear addiction was the dark centerpiece of his life until recently.

He's grateful for all the "safety nets" around him ... and for the hit sitcom, which he says gave him outlets for help when needed. Now he wants to spread the word to others.