Okay, so quick backstory time about how Flarity happened in this canon:
Fluttershy was going through a very rough time with her previous marefriend, she always wanted to have a child of her own, and seeing her friends having some of their own made her even more eager to have one, so she found a sperm donor and conceived Florence with the consent of her partner at the time. Their relationship didn’t get any less toxic even after Florence was born, so as a good friend, Discord felt the obligation to intervene (along with the rest of the elements of harmony) and convince Fluttershy to just end it and let go, as it wasn’t doing any good for both her and the kid. When she finally got out of it, Discord and Rarity were the ones who helped Flutters heal the most.
Meanwhile, Agate was the product of Rarity’s previous engagement with Fancy Pants and was conceived as the last hope for their doomed relationship. Turns out having a child wasn’t the answer and they ended up going separate ways with their lives and businesses, however, they remained in good terms with each other. Rarity took this separation as a way to get to know more about herself and to spend more time bonding with her daughter, having a break from her business life and letting Sassy Saddles and some other employees take the wheel for a little while, though she didn’t stop playing her part on the creative side. Fluttershy was the one who helped Rarity the most during her pregnancy and after Agate was born, and during the time Fluttershy was going through her healing process, they reconnected, and a spark of romance was ignited even before Rarity and Fancy Pants’ relationship ended for
real.
By the time the series ended they were probably close to engagement, eventually marrying and joining their families together.
Also Discord’s still a very close friend of the couple and helps them and the kids whenever and in whatever way he’s able to. He loves spending time with the kids, specially Agate, who finds his chaotic energy quite amusing.