This might be the first time I say something somewhat negative about Kaija. But I don't disagree entirely exactly with you saying "I don't think you're entitled to someone's secrets just because you're dating them". Especially when the full truth is something most would not believe.What tyranny? They're a hidden society that seems to specialize in organizational paralysis. It's unclear they could dominate the local coffee shop even if the MC's father was around to break ties.
I don't think you're entitled to someone's secrets just because you're dating them, especially not secrets that could literally get people killed. As ThorinKing said, the ring is symbolic because marriage is generally considered the most significant commitment you can make to another person; that's the point at which all your cards should be on the table (even if a few of them have to be kept face down for security purposes).
Kaija and the MC weren't even officially dating, so I don't find it surprising she didn't spill the beans on the hidden world to the MC. That's a life-changing revelation if ever there was one. If their relationship had continued to deepen then I agree there would come a point where she'd have to confess the full truth, but they weren't there yet. From what the game shows, it's unclear whether they would ever have gotten there had fate not intervened.
IMHO, the only truth Kaija absolutely owed the MC at the start of the game was to be honest about her feelings for him. Unfortunately, her honesty on that crucial matter is retroactively governed by our choices, which makes it very complicated to assess her blame in a consistent manner.![]()
But when being selfish and entering into a romantic relationship as the MC's girlfriend. I think she should of said something / explained a bit better why she is gone all the time. Even if it's still a lie I think hiding a truth with a lie that is similar or close to the truth is still better than nothing. As to me that would soften the blow wouldn't be as bad when the full truth comes out while that is still a lie it wouldn't be entirely untrue either if it was close to the truth. Especially if it was something close to the truth and as the truth isn't something most people would believe without proof and she cant exactly show the MC the proof either without consequences.