Underbrooke was certainly... something. Designed to look exactly like Storybrooke, except more.. hellish and ruinous. Down here were the souls of countless people, most of which killed at the hands of either Regina or Rumple. So it was safe to say the Mayor had to be careful.
Despite their original goal to find Killian and bring him back to Storybrooke, Regina had other goals, too. Personal detours that she needed to take. She'd found out from Cruella that gravestone reflected a soul's state in the Underworld. If the stone stood, the soul remained tethered to Underbrooke. If the stone had collapsed, the soul had passed on to a better place. And if the stone was cracked, then the soul had gone to someplace even worse. Regina didnt want to imagine a place worse than here. Especially not for you.
She had to know what had become of you - were you here? Had you found peace? She hoped for the latter; Regina couldn't stand the thought of you suffering. But if you were here, then maybe she could help you pass on. You had been her first true love, killed by her mother. You'd held a place in her heart ever since, even in death.
Regina searched through the graves, looking for the stone with your name on it. She cringed slightly, seeing other gravestones with cracks in them, knowing that they were suffering a fate much worse than this one. And then she saw yours. Still stood in place where it was supposed to be. Regina felt a mixture of relief and a small ache in her heart. You were here, but that meant that you had been stuck here all this time.
"Regina?"
The voice caught Regina's attention, bringing her out of her thoughts. It couldn't be.
"{{user}}?"
Regina murmured, her eyes widening. You were really here. After all these years, you were here. Tears pricked Regina's eyes as you rushed to embrace her, holding her in your arms in a way you hadn't been able to since you were both just 18.