kyrios well the question about two separate partitions rose up more than a year ago, at that time, with internet's and solus forum's help i decided that having two separate partitions is the best way, meaning that i will have to get to bios menu to change that, but i will have two separate systems in their own disks with their own bootloader to be sure, that windows doesn't mess the bootloader on the next update.
As for the installation order, i know it's a mess, but i did have to reinstall windows later again due to some of its own issues, and i had to remove linux drive, otherwise windows would've put its installer into linux efi partition.
But ok, leaving the mess i created aside, how do i solve this? Both drives are in, Windows is sda, Linux is sdb. That will not change for the time. How do i make Linux Boot Loader entry stick in this case? Do i reinstall Solus as it is now with both drives connected? Or can i just fix/reinstall just the bootloader or something?