Gary is a man caught between two women. If you're thinking that sounds like a good problem, though, then think again because the two lovely ladies in question are Enid and Caroline: his mother and his wife. Gary never cut the cord, so to speak, and now he's faced with a decision—should he side with his mother or his wife? Even after he makes his choice, however, Gary is faced with the realization that it might have meant less than he thought it would.
Gary is nothing if not a momma's boy. As a young kid, he would spends his nights "enduring a dull thing that brought his parents pleasure," even though he knows that all he's doing is preserving "his mothers' illusions" (4.248). He has become convinced that bad things will happen if he fails to do so.
As Gary becomes an adult, he manages to silence that emotionally needy child except where Enid is concerned. Caroline observes that he pretends to "live some way she approves of" (3.543) and Gary himself even admits that he built his life based on what his mother "taught [him] to want" (3.899). In other words, though he now has a wife, Gary is still preserving his mother's illusions to this day.
Everyone has to grow up sometime, however, and Gary is forced to choose between Caroline and Enid. It's not so much which choice he makes that's surprising, as it is how aware he is of its implications. We can see evidence of this in Gary's sudden belief that Enid "knew that he'd betray her" (3.1078) by letting Caroline stay in Philly. To be clear, Enid never says anything to this effect—this is a conviction entirely generated within Gary's brain.
It also doesn't hurt that Caroline is associated with everything that is attractive to Gary. She's from the East Coast; she comes from money; she's extremely good-looking. Gary probably believes that this is his final transformation—from Enid's boy to Caroline's boy. But that's only half of it.
Amid all of this, Gary is fighting the realization that he's becoming more and more like Alfred. He starts to treat his wife like Alfred treated Enid when Gary lived at home. He also feels depressed all of the time, and he even has occasional hallucinations during stressful periods. Though Gary might be surprised to come to this understanding, it only makes sense that he'd grow into the man who chose to spend his life with Enid.
Despite his polished exterior—he's professionally successful and has all the trimmings that go with this—Gary is a wreck. Which brings us to one final way he's like his father: It wouldn't be hard to imagine Gary leaving this world just like Alfred—and we're sure Gary doesn't have any difficulty picturing it either.