While I do agree with your points; the only thing I feel off about this whole senario is that he was fine with just letting her go and if she came back she came back. He wasn't originally doing anything to get her back until Hyundo came into the picture. Iseon was put into senarios with her and chances because of other people. I'm not saying his love wasn't true, but it's like that saying "You don't know what you have until you loose it.". He's on the verge of loosing her and now we talk about the reasons/troubles. I'm hurt for Yoomin because I would hate to be in this situation. Her goal was to get back together with Iseon but ultimately started to let those feelings go and move on because she had Hyundo. She knows what's in store with Iseon and what could happen mature love or not, it's a safe choice. Hyundo isn't stable love, he's dependent so it's like...actually are either really stable? If one doesn't express his feelings truly (which is hard!) and the other one will give everything and not think of himself?
IDK anymore...I am still rooting for Hyundo though, I do not want him to run back to his toxic ex!