"Lamar checked into rehab last week. It was his decision to go back," a source tells ET. "He wants to get better and recently realized he needs to do this for himself, and especially for his children. He knows he needs help and unfortunately, this is something he'll need to take care of for the rest of his life. Drug and substance abuse is a serious issue."
The source adds, "His family and friends are standing by him through this and know he will come out as a better person."