I was one of those moms. Now I really am a single mom.
Those comments do sting now. I had a friend do that recently, and yeowch! But it's better now ibeing single in some ways. It is scary, and tough, but I no longer have that resentment about him not helping, not caring, not being available to help. I no longer wake up each day hoping he will finally be the helpful loving husband I craved. I no longer deal with that daily resentment.
As hard as it is, I relate to those moms because I was one and I see now that his lack of engagement in his family was one of the main causes of our marriage ending.
Now I resent other things, like losing the dream of what married life could have been, or him not valuing the kids as much as I would like when he is bringing the kids home early from his infrequent visits because he's bored
But I NEVER said I felt like a single mom TO a single mom. I can see that would HURT!!!! (I may have said it to a married mom once or twice though!)