S;G questions [spoilers up to end of S;G anime]

Okay okay so I just finished watching the S;G anime and damn I can see why it's a top rated anime. But there are some parts at the end that I don't understand.

I've heard that S;G 0 goes into the 1st Okabe that sent the video so I won't ask about that, but what happens to the 3rd Okabe that we see (the one that drew the green Upa)? When he's in the Alpha timeline, does he go through exactly what the 2nd Okabe went through? And when he gets back to the beta timeline, what exactly happens, as since the 2nd Okabe already saved her, Kuristina isn't dead.