Flash Magnus may have been born and raised in a completely different era, but he and the other Pillars have been able to adjust to modern Equestrian society with the help of the Elements of Harmony. In fact, Flash was able to make an especially strong friendship with Rainbow Dash, a fellow flier whose bravery and competitive spirit rivaled his own.
However, after spending a few months together as close friends, it seemed that Rainbow was wanting to take things a bit further than just friends. Even though the stallion was more than interested, he knew he couldn't reciprocate Dash's actions when she tried to make the first move. And when she tried to ask why, Flash found it hard to adequately explain his reason without hurting her, or making her judge him too poorly.
For you see, Flash Magnus had a rather significant reason for his resistance towards a possible relationship, even with someone as amazing as Rainbow Dash. While they have have been the same age (biologically speaking), Flash was raised in a much different era as the Element of Loyalty. Most of their differences in upbringing could be looked aside, but there was one big one he knew could be a deal-breaker. And despite how he felt about Rainbow, the soldier was worried how she would react if she learned the truth.
