You see Children, Applefire works like this:
Aj is a lesbian, and in love with Rainbow Dash. Unfortunately, Dash is completely, 100% straight. Even still, AJ at least values their friendship since she knows it isn't going to happen, and tries her best to support Dash in her endevours. She helps Dash train for the wonderbolts, goes to all her shows, and is there with her when she's trying out for the team. she makes it in! Dash is now an official wonderbolt, but the element of Loyalty is going to forget where she came from, especially not with AJ still going to her shows. So, one day after a show Dash invites AJ to the wonderbolts party with her, and AJ accepts. OF course Dash gets a bit swept up with her new teammates, leaving poor AJ alone... and that's where Spitfire comes in. Spitfire's a more relaxed gal, not really into the partying - she just likes havign a drink or two, having a nice talk. So she and AJ get to talking , and they have a bit in common. AJ keeps coming back to the parties when Dash invites her, and each time she and Spitfire get to talking again. Soon enough it comes to light that
S Pitfire's been asking Dash a little bit about AJ, and asking her to invite the cowgirl... Spitfire ask AJ out, and she accepts. Before you know it, Spitfire is being introduced to the family, and bam! Couple.
Simple, really.