It's generally considered cheating when one partner doesn't disclose the existence of their other partners. I suppose if he's told everyone "Just so you know, I'm dating a few other women but I'm not going into details" then he's off the hook. But ideally, everyone should at least know everyone else's name.
And just for terminology sake, a quad would mean you're in a relationship with the other two women. This is a three-armed-vee.
Gralson: my husband
Auto: my girlfriend