Need ur opinion on cheating..?

i know this guy who has 3 kids..his girlfriend recently gave birth 2 a boy. Lately he sends me messages and says how he wants to be with me and see me. Mind you i despise his girlfriend cuz she is constantly talking crap about how good and innocent he is. So my ques is would u tell her even though she recently gave birth and is in a fragile state of mind? And since its just talking would she consider it cheating?