Well in the future make many save files to not make bad decisions. Here are ways to raise trust iirc: Give money to a man in Dorgania’s capital, help person in northeast of the capital, do quest for Queen of Dorgania, say you do not support slavery to King of Dorgania, send slaves to your castle (not dungeon, brothel or anywhere else), i think helping a slave in Dorgania castle also raise it. That’s all i can remember
Anyway, if you cannot find any ways to raise Brad’s trust then just start a new game. I have “speedran” the main quest in about 1 hour. You only need 35 trust to continue the quest and every raise in brad’s trust is 10 I believe. Btw if you have played 70 hours then I think you can start a new game easily.