Huh, I guess you could technically call this netorare. I mean the daughter is stealing her mother's husband but if the wife never finds out wouldn't it be just cheating? I am confused...
That title and that description certainly tell you all you need to know.
So the wife doesn't know, huh? I suppose that's what makes it NTR? He seems willing to keep supporting them both though.
That ending...Yes indeed, I'm sure mother will be thrilled to join in.