Cheating and how to move on

I just got married may 12. While we were at the beach on our honeymoon this former coworker informed me that she and my husband had an affair a year and a half ago while we were together. I checked his Facebook and found messages confirming the encounters. He said it was one time but she says it was a relationship lasting nearly 6 months. I am completely devastated and he has complete transparency right now and is trying but it's so hard to get through a day without tears.