That is very doubtful after all Aron is a very jealous guy. I highly doubt the boy wants anyone else to fuck his mom, even spanking her for David. It seems that Daval wants to give Aron more development. That boy reminds me a bit of Daniel, after all he fought with David and it seems that the one who came out better was Aron.
I think there's some residual resentment over the number of partners Sarah has had in this series. I, too, think it's doubtful that Aaron would foolishly clue in anyone else to what he has done, and what he is about to do with his mother. As you stated, he's jealous of David; he also hasn't mentioned anything thus far, showing he's aware of the inappropriateness of his mother's trysts. If the statement was made in reference to Aaron's remarks before he spanked his mother, those, at least in my opinion, were clearly lies. The "friend" of whom Aaron spoke was obviously a placeholder for himself, showing Aaron's talent for manipulation--not to mention, Aaron's manipulating his father using his hemophobia to clear the room, an act with which Sarah was visually impressed. I think Sarah's reference to "Ms. Gomez" was just Daval plugging for one of his other V.I.P. comics, just as he did in Chapter Three when "Hazel Harris" was walking on the motel balcony.
I think most of David fans aren't fueled to rage as it concerns Sarah's involvement with Aaron, as they were when Sarah was involved with her uncle, Peter, because: (1) Aaron's her son, and (2) I would confidently presume that the David fans prefer the Oedipal nature of incest, as opposed to incest in its entirety. And no male character satisfies the Oedipal fantasy in this series more than Aaron does, though admittedly the appeal is somewhat diminished knowing that Sarah was "worked out" beforehand by three different males, albeit her male relatives. I think Aaron is going to be somewhat of a cross between Uncle Peter, and David, i.e. he's going to be somewhat passive in some instances, but take control in others. And yes, Aaron did come out on top: hopefully he adds his mother to his shelf of trophies along with the shiner he gave David, haha!