Dual boot Win10 and Win 7. Win 10 Hijacks win 7, and won't play nice.

Hi and good morning. I am a noob with Win 10, and am doing what I can to figure it out.
So here's the skinny. Win 7 is the default on Drive C. Win 10 is on Drive D.
When I boot into win10, it automatically renames the D drive to C and makes itself the default.
So after a few hours of using 10, to switch back to win 7, I have to reset the boot because win 10 tries to come up first even though it is not default.
This is excruciatingly annoying. The only reason I have Win 10 is because of An Occulus Rift I got for Christmas!
(My wife really Loves me...or not)
Otherwise I would happily Fallout on win 7.
I searched in vain trying to fix this dilemma.
Any advice or direction would be appreciated.
Thanks

open a Command Prompt (Admin) or Powershell (Admin) in Windows 10 and run:
powercfg -h off

Are Drive C: and D: two different partitions on the same disk or are they on two separate disks? If on the same disk then that might be the problem. If you already have a second HDD/SSD installed (maybe for backups?) then try putting W10 onto that disk.

Other than that it is probably Microsoft (MS) 'forcing' you to use Windows 10 and I don't know how to stop MS doing this. They have been trying all they can to get people to switch away from previous versions over to Windows 10.

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Have you looked in "System Configuration"/ "Boot" settings? Ensure that C: refers to Windows 7 OS. Also there is a setting "Make all boot settings permanent". Maybe you need to tick this?

We need a screenshout from disk manager showing all the details if you installed 10 when you had 7 it may have put boot drives on another parition. the boot drive is always set to c