Because Lord Wei and the Empress were in love before and the Emperor knows it. So he abandoned his martial skills…
No, he is in love with the Empress. You can check it again. In the drama, when they were young, they were separated because the girl will be the future Empress. And the person he looked with longing at Sangbo lake is a different person than Duke Yu's wife. I recall the Empress's facial features is a bit softer than Duke Yu's wife.
Does anyone have any theories why Mr. Wei sealed his martial arts skills after he established the Guardian Yamen?…
Because Lord Wei and the Empress were in love before and the Emperor knows it. So he abandoned his martial skills to ease the Emperor's worry. You can see that the Emperor hate it when someone is above him. Lord Wei is afraid the Empress will get implicated if the Emperor finds fault on him. So yeah, "let me be weak myself so you don't need to drag me down."
The CP will be the emperor before GP. But because he is too meek and afraid of battle, he was deposed from the throne by XQA and GP. Then GP ascended the throne.
https://www.youtube.com/watch?v=ZPMDuF_cA28
There's no confirmation for S2. Fans just speculated since one season can't cover the entire novel's arcs.
She was r*ped on the way and committed suicide. Heng Hui is very likely to seek revenge for that.