Dobby was working but was constantly complaining about it. Prior to the move to janitor apartment, he was working in a video store where he seemed to goof off a lot. Then the move happened and while apartment was included with the janitor job - he and the gf needed second jobs to account for their needs. Gf quickly got something, Dobby got one of his first airport jobs later. They seemed to be on an arrangement where she worked in the day, and Dobson worked some nights but was expected on his free nights to do the janitor stuff.
To be fair the girlfriend wasn't an innocent in this, in the apartment prior, Dobson already mentioned they lost deposit on leaving previous apartment as their cats had dumped on the carpet. It was up to both of them to make the janitor job work as well - but it seemed to be that Dobson's gf was working more hours while he insisted he needed free time to work on his comic projects. But because he was trying to work on his comics while also doing the night jobs he wasn't resting enough and both jobs suffered.
But yes, in the end it's mostly Dobson who cost them the swank apartment. When management told them them to shape up, he - in the way we all know and love - doubled down on his actions insisting the management was being unreasonable in expecting them to uphold their terms of residence. They gave themselves so many months to move out, but Dobson couldn't even manage that so his girlfriend, had to rush to apply somewhere that would take them.
Then once they managed that, she got work and he had to look again, has to beg mom for car repair cash and then gets a parking ticket on the way to an interview. Which eventually leads to the infamous airport janitor job where he gets himself sacked by complaining constantly and a ill considered flipping of the bird.