No one can tie down Sub-Zero!

Where's Sareena?

This whole thing with Sub-Zero and Frost is completely made-up (that’s nothing new) since she didn’t show any signs of having feelings for him at all. Sub-Zero (Kuai Liang) has shown to be a very caring and simplicity character.
"With his freezing powers enhanced by the medallion, he vowed to reform the Lin Kuei as a force for good."
Mortal Kombat: Deadly Alliance Bio

But Frost turned into the complete opposite, she turned into nothing but an arrogant self-interest lying backstabbing murdering bitch, her Deadly Alliance ending proved that.
"As they traveled back to the portal that would return them to Earthrealm, Sub-Zero revealed to Frost that she had been an integral part in the destruction of the Deadly Alliance, and that he was proud to have her as a member of the Lin Kuei clan. But unknown to Sub-Zero, Frost's true intention for joining the Lin Kuei was to become Grand Master herself. She used her ice blast to temporarily immobilize him and ripped the Dragon Medallion from his chest. As she held the medallion, she felt power surge from her body. Lacking the strength and discipline required to control the medallion's immense power, she was consumed by her own freezing ability."

Unchained: "Sub-Zero returned to Earthrealm only to find many of his clan slain by Frost. She had come back to the Lin Kuei temple with the intention of killing only him, but she was now delirious and saw Sub-Zero everywhere. Sub-Zero blasted her with intense cold, freezing her until she could be revived and cured of her dementia. He laid her on an altar in the chamber of fallen Lin Kuei and sealed the room with a wall of ice. Frost will one day recover. When that day comes, she will have to answer for her crimes against the Lin Kuei."

She joined the Forces of Darkness and stated "The Lin Kuei will be MINE!"

In her non-Canonical Armageddon ending, "Her strength increased, Frost once again took the Dragon Medallion from Sub-Zero and enhanced her freezing power far beyond her former mentor's. Traveling to Outworld, she located the tomb of her ancestors, the Cryomancers, and planted their souls in the bodies of the current Lin Kuei. Her army of Cryomancers conquered the realms, leaving each of them a frozen wasteland."

The MKX comic and 2015 video game showed that her attitude and personality didn't change. Frost was just as out of control, uncaring and untrustworthy as she was in the original timeline. To the point where Sub-Zero had to freeze her.

this MIGHT JUST BE something that my brother told me but i think that frost is sub zero's sister so not frost either kitana or jade

... Well your brother is wrong, they are not brother and sister... and yet Sub-Zero has had little to no contact with Jade or Kintana. But nobody here is going to base there choice on facts and events from the MK games.

What? No way :P