I think Ethan giving her the stone more has to do with solidifying her position and giving her something that could act as protection. Ray hasn't done much to protect Dorothea and people still openly hate her and try to harm her (ex. the blue-haired creep). Also if she has the power of the spirits and is accepted by nobles and the masses, her father can no longer touch/harm her like before (Ethan's setting her up to become the 'people's princess').
Now regarding Theon, I don't want to make any definitive statements because the translation is a little confusing but from the flashback, it seems that he was scheming from the beginning. He may or may not have been Ray's friend for his powers and he purposely led Dorothea on and married her to secure a position close to Ray and within the palace. In my opinion, it was unneeded and cruel. He was close to Ray and Ray is hella soft, he would have been willing to help charge Theon's batteries anytime. Tricking Dorothea into marrying him, withholding his love (the man didn't even pretend to love her and made her feel like she forced him into it even though HE is the one that tricked her), letting others call her a tyrant, trash talk her and not defending her, blatantly cheating on her, and then purposely k*lling himself in HER room to scar her (not because of her actions either, so again he used her as collateral damage to hurt Ethan) is SUPER messed up.
I can't help but NOT trust someone who did countless messed-up things and didn't even regret it (at no point did he think or care about Dorothea's well-being- heck they could have shared the freaking gem the 1st life but he clearly wasn't going to ). I think the thing that's implied is that he wasn't someone who 'acted/changed because of his circumstances,' he was always selfish and never cared for Dorothea's wellbeing. So I feel like if they gave him the gem, he would again use for it selfish means even if that meant Dorothea was put into harm's way.
Omg yes I was just talking about Theon's snake behavior, I totally agree with you!! At first, in the second life, Theon seems like he cares for Dorothy, maybe he does on some level. But now that the first life is revealed, he's definitely not trustworthy.
The way I see it, his number one priority has always been the Spirit of Darkness, only in the second life, he doesn't have the super vulnerable and inexperienced Dorothy to use as a means to an end.
Instead, in the second life Theon can't help but to notice her, because she's enduring hardships that she tries to hide from everyone else, like Theon is as a kid. So at least in the second life I think Theon is kinda genuine in his interest in her, but he def does NOT deserve her.
I think what's also a major point to consider is how hard Theon tries not to let Dorothy to know about his condition in both lives. In the first one, at first it's of guilt (at least he knows it's wrong and has thought abt telling her) but later he keeps her in the dark to leverage against Ethan. In the second life, I'm not so sure, it seems like Theon is interested in her and so doesn't want to show her his bad sides, and he tries to deal with it with crown prince's help. ( I might be misremembering, pls lmk) Does Julia know in the second life about Theon Spirit of Darkness btw??? Bc I can't remember and it would also help explain a few things why he's different from first life. Because first life Julia knew about it, is helping him, so Theon relied on and dated her. Also u know, easier to just keep doing guilty stuff if u have a partner in crime to back u/enable u. Seriously Julia, hooking up with the empress's husband smh. If Julia doesn't know in 2nd life, maybe that's why Theon keeps eyeing up Dorothy now?? Because he doesn't have anyone to help him find the stone and plus the emotional connection from being in the know isn't there like in first life.

Hmmm wouldn't it benefit everyone if they gave the stone to theon? Lol idk ╮( ̄▽ ̄)╭
Like they'd still be friends, also mc is in the process of moving on.
It would cure whatever shit theon is in right now (maybe) so he doesnt die and so he doesnt affect his surroundings due to the spirit of darkness killing everything
She's in the process of doing better without the spirit of light and everything that comes with it (like letting go of that asshole of a father, knowing what a family is thru the people she's with, becoming closer to her brother and her not being as jealous and her inferiority about it lessening. That she can do things and help people albeit with the support of his brother aka the disability support facilty etc)
Like I can see the stone starting chaos again if imbued(?) or given power to MC. She'll have more legitimacy for the throne(even tho we kno her brother may giver the throne given their relationship rn) so their will may or may not be fights about it,
more daddy issues again. Theon may or may not destory things in the area and he'll still be dead (maybe) if nothing bad happens to Ray in the heir dispute