
You know I read a similar story before I got to this manhwa . It's a popular one
I picked up the 2nd ML after the ending
The scenario was exactly the same ....the 2nd ML committed crime n his best friends ML and FL abandoned him n sent him to the coldest region to live in exile. Feony the MC , she didn't went to take revenge against them , she just simply go to The 2nd ML to give him happiness. When he became happy with his life , issues between 2nd ML n his best friends after few talks immediately got resolved but in this case I feel things could have resolved in a better way . Now suddenly Diana is abandoning her plans of revenge n all because only now she is ready to accept her reality after everything n every planning she decided to do . Just like I didn't like the FL of that story , I don't like Hestia aa well but still there really was a better way to handle everything.

Even when Hestia didn't intervened, Diana's life still imploded (cause she wasn't worthy of her powers anymore, she helped cover the corruption of the temple and eventually ended up getting a divorce) so I don't think it's as much "destroying the other characters happiness for one character" but "let's make sure this guy doesn't end up dying after being treated awfully by a couple that isn't even going to last anyways"

It's also about giving her the ending she really deserved. Diana was a bitch who thought she was better than everyone because of her powers, thinking she was the chosen one. And you're right, the reason why she lost her powers is most likely because the god wasn't happy with the way she turned so selfish and shallow. So that explains why the god wasn't mad at Hestia, Diana had already lost the her favor.

You know at the beginning of this manhwa when Hestia meets Diana for the first time....I felt somewhere that there was still a possibility of her not going to the wrong side u know..... somewhere she was influenced by the church and her own believes that she forgot what her actually duties as a saint were. She believed spreading the moral of life away from materialism n living a simple life is what she needs to preach ....well till that time I still believed she could go back to normal or accept her reality now . If Hestia had tried to deal this not in a revenge manner, I think everyone could have had a happy ending
So basically the God of this story was sad that one character ended up with sad ending so to make his story happy she ended up making other's story the unhappy one and now she satisfied?