He was betrayed by only 3 people. Seems pretty believeable to me. If anything, with how long he lived im surprise more people weren't in on the betrayal.

If your talking about it being impossible for her to leave him a shortcut only he would know how to get through though remember that he is her protege. There could be paths in the fog only someone as proficient in Alchemy as him could see. Either that or since the fog is located in a place they have both been to together then there could be land markers that only he would be able to find. She could have kept those places only he would know how to navigate free of poison.

She laid the poison fog after Su Yang died but she talked with Su Yang about her experiments of creating it before he died. Hence how Su Yang knew of its existence in the first place. Remember when Su Yang just said while talking about the fog "When I was still studying under the God of Alchemy, I recall seeing something similar. I asked her about it, and she told me that it was an experiment to create the most powerfull poison pill in the Four Divine Heavens." So while she was experimenting on how to make the pill she could have told him of its weakness too.

If she told him about the poison she probably also told him about the cure. She seemed to share everything with him. Full and unequivocal trust. So yeah id assume either she put a path without poison only he would know how to get through or where its located(or both). Or she told him the only thing that was that poisons weakness.

Im looking forward to the personality's of the women in the Divine Heavens. Especially looking forward to when Su Yang meets the alchemy god again.

Probably because the Author was trying to catch up fast for their privilege readers to make their money worth it. And also to make sure their normal readers weren't too long without being able to read back when they got like 50 chapter behind and we couldn't read for a few days until they caught up. Its giving the author a bit of time to flesh out Su Yang's past and letting us see a more nostalgia filled Su Yang as he see's how everything has changed while he was away and how his supposed death effected those he left behind. Throwing in extra details=more material to fill a chapter so im not complaining too much though these cliffhangers are killing me.lol