The singer released a statement on the Avett Brothers website earlier in the week to confirm that he and Susan had reached a decision to end their marriage.
"My wife and I have decided to end our marriage. We have been separated for some time," he wrote.
"As I'm sure you will understand, this is a very difficult and painful time for us and our families. I want to wholeheartedly thank you for respecting our privacy in this matter and I ask sincerely for your prayers, support and understanding."
His statement was released on the same day as a Radar Online report claimed that Avett started dating his current girlfriend, Dexter star Carpenter, while still married to Susan in 2011.
The relationship apparently began shortly after Carpenter ended her own relationship with co-star Michael C Hall.
"Shortly after Jennifer's split with Michael, she began seeing Seth. She would fly all over to his concerts to be with him," the source claimed.
"No one saw this affair coming from those closest to Seth, but he finally left his wife last winter to be with Jennifer."
Avett married his estranged wife Susan in 2008.