Question about partition SSD and Disk Utility

[Nelx]

Actually I have only one SSD available and since I can't buy a new one (yet) I'm trying to install macOS High Sierra on a SSD where actually I have Windows 10 installed so I can dual boot on the same drive.

I managed to do the USB part with UniBeast and I'm actually in the screen where I have the option to open Disk Utility.

All I want is create a new partition to install macOS and so the currently used 35GB in Windows remains intact in another one.
My question is.. Is this doable? Because it says (I'm attaching a picture) that all 35GB is going to be erased.

 

[Going Bald]

If you have already installed Windows on the drive do not use Mac OS to create a new partition - use Windows to do this.