Gilbert had lied, of course, he went to visit Matthew that night. And then again soon after. And then a few more times. And then more than just a few, until it became a regular thing. He told Matthew everything about their first life together, how it had ended. Showed him the scar that shouldn't exist, but did anyway.
And then one day, a few years later, Matthew told his family he was leaving. Left his family and both his kingdoms behind in favor of a new life that no one else knew about. Well, one other person.
"Birdie," Gilbert groaned as Matthew kissed him awake.
Matthew laughed. "Wake up, your Grace, you have responsibilities, remember?"
"Birdie, you're never awake this early. I think you're plotting something."
"We should do something today. We never do anything together."
"We do plenty of things together! I just took you to the ocean!"
"Two months ago!" Matthew corrected.
"Huh," Gilbert laid back down, "I need to get a better grasp on time."
Matthew giggled and poked his side, "Next thing you know we'll be old."
"We? You think I'll keep you around that long?" Gilbert joked.
"I think I'll put up with you that long."
Gilbert smiled and reached up to stroke Matthew's hair, "That sounds nice. Getting old together. You really want to do that?"
Matthew nodded and laid down next to him, his head on Gilbert's chest, fingers finding the scar from Vash's arrow, "Absolutely."