Its called a trauma bond and codependency. Just because you think of someone all the time does not mean you are in love with them. They have years of history it takes time to let go.
Look at lucky paradise the uke was in love with his best friend even thought of him when he was with the new Seme, but guess who the uke ended up with..it wasnt the best friend.
Point is, it would be strange if Ian stopped thinking about TJ immediately but its not impossible.
Im not saying Jo can't be uses as a catalyst for Tjian (I would hate it though) but we also need to wait for season 3 and see the direction the author will take.
feel that it is clear who will finish the game.. it is Taejoon and the other ML Jo is used by Ian only to relieve him of his sadness and worries, but he thinks about TJ all his time, even in the story, he loves him very much..(⊙…⊙ )