Kelsea Ballerini Files for Divorce from Morgan Evans: 'Deeply Difficult Decision'

The "Heartfirst" singer, 28, filed for divorce from the "Kiss Somebody" musician, 37, on Friday after nearly five years of marriage, PEOPLE confirms

"They've been working on their marriage for a very long time. Prior to this they had separated privately once before and have been in therapy for several years," a source

"They gave it their best go but unfortunately arrived at the decision to formally separate."

Ballerini addressed the split on her Instagram Story Monday morning, writing, "Friends, I've always tried my best to share my life with you in a real and vulnerable way

This is now public record so I wanted you to hear from me directly that I am going through a divorce.

The country singers first met in March 2016 while co-hosting the CMC Awards in Evans' native Australia, were engaged that December

and tied the knot a year and a half later in an intimate oceanside ceremony in Cabo San Lucas, Mexico