I find this episode very disturbing. Now, it's a given that Charlie is written in such a way so that we are disinclined to feel sympathetic towards him. But in this episode, one of his exes, Chrissy, defrauds Charlie out of thousands of dollars by presenting this young boy and allowing Charlie to infer that the boy is his son, when, in fact, the boy is somebody else's child, whom Chrissy has "borrowed" for the specific purpose of defrauding Charlie.
But Charlie never finds out he's been defrauded, and Chrissy is never held to account for this fraudulent presentation. Indeed, Chrissy reappears late in season seven (as a hallucination) as one of the women that Charlie has done wrong. But what Chrissy did to Charlie seems to me way worse than being loved and left.
Charlie may have been a selfish, inconsiderate, drunken reprobate, but the idea that Chrissy actually commits a crime, and gets away with it, is not a creative decision I would have made.