A break up or Breaking up

Hello,

My English text book has this sentence:

Breaking up is a tough thing to go through.

Then, I asked my friend (NS) if I can say:

1) Breaking up is tough to go through.

He said no.

According to him, either one (below) is fine though:

2) A break up is a tough thing to go through.

3) A break up is tough to go through.

I asked wyh 1) is not okay, then he just said "It just doesn't sound natural."

I understand I just need to remember sometimes, but if there's any rational behind this, could you explain it??

And I'm also wondering if I can say:

4) It's tough to go through breaking up.

I anticipate that I can say:

5) It's tough to go through a break up.

Thank you very much in advance!

-M