Karin had absolutely no reason to lie to Suigetsu. If Karin wasn't Sarada's birth mother, why would she tell Suigetsu that he owes Sarada an apology for misinforming her? If Karin actually was the birth mother and Sarada found out, Karin would not have yelled at Suigetsu in Chapter 700+10. Also, Sarada never found out that Suigetsu misinformed her, so she still might falsely believe that Karin is her birth mother. Regardless, Sarada considers Sakura to be her mother, biological or not, because of their emotional connection.
Furthermore, no couple has ever split up in Naruto, so I wouldn't hold your breath. Sakura and Sarada might be unhappy with Sasuke's persistent absence, but both share a deep emotional bond with him (especially Sakura), so they are definitely staying together.
OP, I'm sorry your pairings didn't work out, but you just gotta deal with it. Even in a fictional story, not everything will turn out like you wanted (unless you're the one writing it). I wanted Kakashi to keep his sharingan and have children in the end.I wanted Naruto and Sasuke to keep all of the powers that Hagoromo gave them. I wanted Jiraiya to survive the fight with Pain. None of those things happened. Also, if you really think Kishimoto is a "sick crazy evil bastard," don't read/watch the stuff he creates. I honestly don't know how you could expect NaruSaku to become canon. I've only been a Naruto Fan for 2 years, and even I could see NaruHina and SasuSaku (and of course ShikaTema) coming from a mile away.