(Based on my own headcanon and the mini series 'Just Keep Smiling', written for 30minuteponies) Fluttershy never had many friends...she was always just too shy, and not used to being in big places.
But when bullies continued to harass her, Rainbow Dash came to her rescue...it was almost like love at first sight for the friendless girl. But, how long can that childhood love last when cracks begin to form? (Trigger Warning: Hint of a forced kiss/intimate contact, no rape)