Soooo this is a small snippet of how the whole “Rainbow Dash and Zephyr are Soulmates” thing went down.
 
As expected, Rainbow Dash was not pleased to find out Zephyr Breeze was her soulmate. As soon as Twilight came over to explain to her the whole Soulmate thing, Dash was mortified. She immediately went crying to Fluttershy, who was also quite surprised to find out her brother was Rainbow’s soulmate.
 
Also as expected, Zephyr was ecstatic to find out Rainbow Dash was his soulmate. It took everyone outside of Twilight’s circle of friends longer to figure out what was happening, as they had to find out from the news rather than the princess herself. Once Zephyr realized the beloved rainbow mark on his back was a sign he and his crush were meant for each other, he went straight to his sister, who already knew everything and did not want to force Rainbow to talk to him, as requested.
 
She did, however, pass on to Rainbow Dash that Zephyr wanted to meet her at Sugarcube Corner later. The mare showed up reluctantly, and ended up leaving very soon after, due to Zephyr unusually being unable to speak a single word. Fluttershy told Rainbow that he was just nervous to figure out that, yes he and Rainbow were actually soulmates, and that she should give him another chance later.
 
At this point, Rainbow was done with the “soulmate bullshit”, as she called it, and claimed that it was not real, and the marks would just disappear soon. So, being unreasonably angry at Zephyr for everything, she decided even though she didn’t want a boyfriend, she’d get one to piss him off and hopefully leave her alone. She met Quibble Pants (yes, he’s blond. I love that headcannon.) one day when he was in town, and asked him to be her boyfriend. He accepted, having been in love with her for a while.
 
Meanwhile, finally getting the courage to talk to Rainbow Dash properly about the soulmate thing, Zephyr purchases some roses and heads off to her house. Where he finds Quibble Pants and Rainbow Dash together. He’s devastated, she’s proud of herself, and Quibble is unaware. Of course he knew Zephyr was Rainbow Dash’s “soulmate”, but like Rainbow, Quibble didn’t believe in that.