The transfer was part of the back story. The author is now telling us what happened from when alek was transferred to Korea I think. Not sure.
Now this makes more sense! Because the ending of the chapter was too weird to be the continuing of the present (where Alek weaseled his way in Ivan’s and Hen’s relationship). Because Ivan and Hen had really gotten to know each other beyond the magnetism of the mark. So their relationship after the mark is removed, at best, should help them remain close enough to be friends or make them want to continue in a relationship. It was the mark that brought them together, but they did the rest of the work.
If you read the raws properly then you should know that if alek didn't have sex with Hyun. He will probably die since he was the one that marked him in the first place. Iván was angry but he knew it had to be done. Alec is an asshole for marking hen in the first place. I don't think it was a threesome, it is more of Alec having sex with Hyun and Ivan just looking at the show. And I think Alex was transferred to another branch.