It's not that he COULDN'T. He did move out in Season 3 to the apartment complex.
Robert explains himself a bit in the episode where Peter's parents kicked him out. He says that he didn't want to be there during those years but had lost the will to escape, pretty much because of how Marie did everything for him (cooking, laundry, dishes).

He shouldn't, they had no kids.
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Wasn't it mentioned that he had some pretty hefty alimony payments?

But this is contracted in season 4.
When Frank and Marie talk about their sex life. They mention the kids are what dragged them down. Then they smile and laugh at how the celebrated when Robert moved into his apartment.
Then when Peter gets kicked out of his parents' house. Everyone sits around and talks about how weird it is when a 40-year-old man is still living at home. And Frank mentions pushing the kids out of the nest when they're young, otherwise you have a 40-year-old bird who can't lift his ass out of the nest.

If you're gonna pretend to cut her hair, at least put some scissors in your hand!

I agree with that. It always struck me wrong that Marie and Frank didn't give Robert back his money if they were going to just jump back in like they never left. Less of a show without it, I guess.

But he along with Amy move right back in. Both are working and Marie and Frank should have repaid the money Robert paid for the house but no M & F just barge right back in and take over. It's a comedy, I know
SkiesAreBlue

I think it's his parents who want him there. Remember when he does move out to a garage apartment with two older people just like his parents? His parents are mad at Ray for talking him into leaving. Marie needs someone to take care of, Frank wants someone to keep Marie busy and to leave him alone. Eventually he does move out.

I've always thought it was just habit and comfort. He's being taken care of so great by his mom why move out?

Robert may be poor managing money. Indulges himself too much and makes loans to friends who have no intention of repaying Robert. Maybe Robert spends a couple of hundred on scratch offs per week down at the news stand?

Holy Sh*t, I just looked up the salary as well, I had no idea they made that much. Living with Frank and Marie I could understand due to his low self-esteem and psychological need for Marie's attention and affection, but I never understood the episode where he is living on bologna and needs to borrow money from Ray to pay his bills, especially when I looked up the salary of a newspaper columnist..

But inconstancy strikes again where they do an episode in season 6 about how he has no money and the only thing he can afford is bologna and orange juice.
I was going to say something about how much higher rent is in the New York City area than in many other parts of the country. And so I looked up prices in Lynnbrook (where the Barones lived) and found that the median gross rent in Lynnbrook is $900 more than I'm paying in the Birmingham, AL area. But then I looked up the salary range for an NYC police sergeant and found that the LOW end of the range is $25,000 higher than my current salary. Assuming the same relative differences existed during the time the show was on the air, Robert should have easily been able to afford rent (especially since I have a family of four and Robert was on his own at the time).
s ofereode, isses swa mg.
Deor

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Ya that makes sense, i guess part of my trouble relating is that I left home at 15.
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It seems to have more to do with Marie coddling both boys. After all, Ray didn't move out until he was 29, and that was because he married Debra.
Both were used to Marie babying them and taking care of them even into adulthood. So it just became easier to stick around. He does move out in season 3 however.
But inconstancy strikes again where they do an episode in season 6 about how he has no money and the only thing he can afford is bologna and orange juice.

If you're gonna pretend to cut her hair, at least put some scissors in your hand!

I don't think they charge him rent Frank has mentioned several times that he provides everything for Robert.

Yeah you would think but he did live on his own for a while, but would it be cheaper to live with Frank and Marie and that all depends if they charged him rent or not.