Character Analysis
Cath's dad is a well-meaning soul, and he loves his daughters dearly; plus he did quite a nice job being a single parent, all things considered. And by all things considered, we mean his wife up and leaving him one day along with the fact that he's bipolar. For those keeping score at home, when it comes to breaks, Cath and Wren haven't caught very many. Neither has their dad, Arthur.
When Cath gets to college and needs someone to talk to but can't reach Wren, "She called her dad instead. He sounded tired, but he wasn't trying to replace the stairs with a water slide, so that was an improvement" (6.159). It's easy to chuckle when you read this, but if you consider the fact that this is pretty much a serious statement, it becomes clear that though he loves his daughters immensely, Arthur isn't always up for being the parent they need.
Like his daughters, Mr. Avery was irreparably damaged when Laura left. Cath sees how out of control his mental health issues got after their mom was gone, and it makes her despise Laura even more. Arthur's drive to support his daughters (he works 24/7 sometimes), combined with his manic episodes, led to a certain degree of cluelessness about their day-to-day lives, though. For example, he knows Wren's drinking, but he tells Cath:
I saw what she was doing… I thought she'd, I don't know, self-correct. That she'd get it out of her system. (29.100)
When Wren doesn't, however, Arthur gets it together, forcing her to come home on weekends, and watching over her when she's there. His brain might struggle to stay in balance, but this guy's heart is one hundred percent on-point, so although Cath worries that she'll end up "crazy" like him, her dad's actually pretty good at getting his act together when it counts. If it weren't for his concern and discipline, Wren might have been one of the many dropouts whose college careers are cut short by substance abuse.
In other words, overall, we've got to give this guy a hand.