Looking back, it's difficult to pinpoint the exact moment I found myself back in the tank. I've spent much of the last two years in despair at Jeremy Corbyn's leadership of the Labour Party, an opinion that came very close to costing me friends. And at the start of the election campaign, I was seriously considering voting Lib Dem, on the grounds that I really, really hate Brexit.

But then something shifted: I decided, grudgingly, to vote Labour. And as the weeks went on, and the manifestos appeared, that turned, gradually, imperceptibly, into something resembling enthusiasm. My spirits soared every time YouGov put out a poll, and I started to notice my hackles rising when anyone suggested Corbyn wasn't up to the job, despite the fact that as recently as April I was saying the exact same thing myself.

And then finally it happened. Something made me angry enough to write a blog about how the media was biased against Jeremy Corbyn.

How did this happen? How, after two years of being called a Blairite slug on the internet, did I end up seriously rooting for Jeremy Corbyn to break down the doors of Downing Street?

Partly it’s that – it would be churlish not to admit this – he’s had a genuinely good campaign. Once he was fighting the Tories, rather than other parts of the Labour Party, I could appreciate his strengths, rather than merely being annoyed at what he’s doing with them.

Partly, too, it's because one of my big concerns about Corbyn had always been straightforward terror that people just wouldn't vote for him. I still have this worry, if I’m honest; but polls suggesting that a fair chunk of people might have relieved it, slightly. At the very least, it’s given me enough hope that 10pm on Thursday – when the exit poll comes out – is very likely to hurt like 2015 again.

And partly, it's that the last few weeks have acted as a refresher course in the fact the Tories are just awful. Theresa May is leading this country off a cliff, with no obvious beneficiaries except her own political career; this would be unforgivable, even if she wasn't so rubbish that she couldn't even get that right. Just as infuriatingly, it's pretty clear by now that the Tories are not being held to the same standards as their opponents. Diane Abbott's mistakes have been endlessly picked over, while equally embarrassing screw-ups by Boris or Fallon or Fox have passed with nary a mention. I could speculate about the reason why, but that'd be pointless, because we all know what it is.

But mostly, I think, the explanation is this: tribalism is one hell of a drug. The liberal-left is my team, and we live in a two-party system – more so now, if the polls are to be believed, than we have in decades. If I want the left to win, and I want Theresa May to lose, that means backing the Labour Party. For all my concerns about Brexit, or whom Jeremy Corbyn may have shared a platform with, for all the stuff that makes me cringe, that means voting for him to be prime minister.

And so, when someone invites me to make direct comparisons between the Tory and Labour front benches; when they talk about voting for a minor party, or otherwise criticise Labour – I can feel my blood pressure rise. The rational brain shuts down; the tribalism kicks in. They're doing it wrong. They're voting for the other team.

I strongly suspect I'm not alone in this: one of the more plausible explanations for Labour's polling surge over the last few weeks is that Corbynsceptic Labour voters have come home. Maybe they wanted to protect the parliamentary party from complete destruction; maybe, when push came to shove, they realised they couldn't do anything else. Maybe they just hate the Tories.

But something I think that both the hard left and liberal Tories have consistently misunderstood about the Labour right is that they're the Labour right. OK, there may have been a few ambitious glory hunters who joined the party in the Blair years, because they were basically centrists who wanted to be government ministers. But people like Peter Mandelson and John McTernan are Labour to their bones. They're no more going to vote Tory than Billy Bragg is.

Tribalism may be irrational – but it's one of the most powerful forces in politics. (Witness the strength of the SNP's support north of the border.) Anyone still thinking about splitting the Labour Party after the election would do well to remember that. They won't just be giving up short money, or the electoral advantages a big, broad party has under first-past-the-post. They'll be giving up the emotional ties that mean that, when polling day comes round, doubting voters still feel the twitch upon the thread that brings them home.