"There’s no third party involved. They just drifted apart over time," says the friend. "There’s no animosity whatsoever – they are on friendly terms. "
Melissa, 48, and Tammy, 35, separated four or five months ago, says the pal, but continue to put their kids first.
"They’re co-parenting their twins [Miller and Johnnie Rose, 3],” says the friend. "They are living apart but share custody of the kids. "
Melissa will continue to co-parent her kids when she hits the road to promote her 10th studio album, Fearless Love, due to be released April 27.
Etheridge is also the mother of two children, Bailey, 13, and Beckett, 11, with former partner Julie Cypher.