I've been enjoying the series so far, but realise I forgot something HUGE. What did the doctor do to betray humanity?

In the original series?

Because, I put those on my Netflix queue and so many people have them out that they've made them unavailable or something. (So I don't know.)

No, in the miniseries.

It starts off with a big massacre, doesn't it?

I think he provides either the technology or the intel that allows the Cylons to massacre the humans.

I'm assuming he had no idea what he was doing -- did he provide the info to his Cylon girlfriend, and then back himself into a corner?

Yes, that's how I remember it. He had no idea that she was a Cylon.

After the massacre when everyone is fleeing in the ship he's either being controlled by Sexy Cylon or he's hallucinating she tells him to say he has test to prove who is a Cylon, when he actually doesn't and she tells him to finger this one guy as a Cylong.

this guy turns out to actually BE a Cylon, but our doctor doesn't know .

There might have been somehting else but I'm drawing a blank.

I thought something had happened before that, to make the massacre possible, in which he was implicit. I guess it was the info to whatsername.

I can't remember. I know he invented or discovered something and maybe that's what helped the Cylons destroy the world.

Yes, but what made it a betrayal was selling it to them -- and I think that the blonde cylon duped him into doing that.

(He just thought he was betraying his country or something.)