"
think the worst is a broken heart
What's gonna kill you is the second part
And the third, Is when your world splits down the middle
And fourth, you're gonna think that you fixed yourself
Fifth, you see them out with someone else
And the sixth, is when you admit that you may have messed up a little.
No there's
"First, you think the worst is a broken heart"
He's saying that you're going to go through a 6 step phase of after a breakup, which first will be the broken heart trying to get through a breakup.
"What's gonna kill you is the second part"
Going through that phase times will get more harder by time, so hes saying that the more you think about it and go through the phase it will get more difficult to have trapped in your mind.
"And the third, is when your world splits down the middle"
Third step of the phase, will be after that time its more hard than it is before. So your world seems to split in half with a good half and bad half so it isn't the worst yet.
"And fourth, you're gonna think that you fixed yourself"
You are trying super hard to get over the breakup and that, but you "think" you fixed yourself by trying to forget about it but you still think about it usually, but you haven't gotten over it yet.
"Fifth, you see them out with someone else"
When you see them with someone else, you realize how much you missed that, and so you wish you could get back together with who you broke up with.
"And the sixth, is when you admit that you may have messed up a little."
You realized you messed up and you miss being with the person. But there's no more chances to get back together with them because they are dating another person.
It's basically a 6 step phase you will go through after a breakup I suppose.