Rainbow Dash gave birth to her son Pastel Sails and disappeared. She told none of her friends she was pregnant and had no part in naming the little pegasus. Perhaps she would have never met Pastel if not for Double Diamond spilling the parentage to Scootaloo who was judging a young surfer's competition.

"That Rainbow mane is uncommon. Get to talkin' Snowflake."

So Pastel is brought to the attention of the Mane Six. With understanding but insistent support, Rainbow becomes a part of Pastel's life. In Dash's haste to find ways to relate to her son, she falls back of her claim to fame. Her flight and her ability to teach Pastel to fly. This could be what bonded them and got Pastel out of the ocean and into the sky. But lo' and behold, thanks to his lesbian aunts Blossomforth and Night Glider were ever so diligent in teaching baby Pastel first to ride clouds, then fly using a cloud and lastly fly with his own two wings.

"You don't need me" Rainbow whispered as Pastel measuredly free-fell beneath her.

He didn't in more ways than one. She'd seen her little foal run figure eights between his fathers' legs. He cantered between them offering Double Diamond a bite of his ice cream and Featherbangs a hoofful of forget-me-nots. Feather grabbed a pair of pineapple shaped sunglasses and parked them on Pastel's snoot. Double Diamond gently scolded Pastel Sails after the little pegasus had purposely poured his soda on the ground to study wasps.

They were a family, and she had no idea how to how to become a part of that.

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Rainbow feels a lot of guilt in many of her relationships. Truth is, after joining the Wonderbolts and being recognized as a saviour of Equestria, her ego well and truly exploded. Overnight she was now unable to leave the house without being recognized and approached. She did a lot of deplorable things as she began to believe she was invincible.
She feels a lot of guilt for those days and actively tries to be better.
Her relationship with Pastel Sails is an ongoing issue. Rainbow's a deeply flawed woman but always try to do her best. Sometimes she prioritized her loyalty to the other Elements of Harmony so traditional romantic relationships didn't mesh well.