Let's go all the way back to 2008, when Taylor's hair was still curly and Demi still had that fringe. The two were BFFs.
Tay was also super close with Miley Cyrus and Selena Gomez.
In fact, the four of them were a pretty tight squad. It's important to note here that Selena and Demi were friends since they were both 7 years old and starring on Barney and Friends. Miley had been friends with the pair since the mid-'00s, when they all had their own Disney Channel shows. Then Tay came along and joined the girl gang, probably after starring in the Hannah Montana Movie with Miley.
So young. So innocent.
Also in 2008, Taylor briefly dated Joe Jonas, who we can assume she met through Miley/Demi/Selena.
We can assume it was smooth sailing for Demi and Taylor through 2009.
And here's a tweet which is probably Demi saying that she likes the song "Breathe" from Taylor's 2008 album Fearless.
Aaaaaand here's Taylor giving Demi mega love for a music video which was almost definitely "Don't Forget".
But in 2010, when a fan asked Demi about Selena, she threw a bit of shade Taylor's way.
Most people watched this and assumed that Taylor had somehow ~stolen~ Selena from Demi, and that Demi was no longer friends with either of them.
Then in mid-2010, Demi and Taylor's ex, Joe dated for about a month.
When Demi entered rehab in late 2010, she said Taylor was one of only a few people who contacted her.
In early 2013, Demi fired shots at singers who use boyfriends to sell records.
Later in 2013, she told Company magazine, "I don't care about Taylor Swift's love life".
Skip forward to December 2013. Selena uploaded this screenshot to Instagram of the three girls Facetiming.
But then halfway through 2014, Demi unfollowed Selena on Instagram and Twitter.
Meanwhile, at this point Tay and Selena are still BFFs.
Though Selena and Demi reconnected late last year...
...she was noticeably absent from the Swift Squad Takeover of 2k15.
That brings us to February 2016 when Demi called Taylor out on not publicly showing support for Kesha after her court case concerning music producer Dr Luke.
Demi is following Taylor on both Insta and Twitter, but Tay is following her on neither. Make of that whatever you like.