I think we are all worried that Inseo will get really controlling. It's already coming off a little manipulative.
Also, the way Lee Hyeok is describing it, it's literally everything. it's incredibly unusual to keep to just themselves. To not want to hang out with friends with both of them together. That's a level I don't think I've seen before in a yaoi.
It's just a little extreme.
As you said your anxiety gets bad for certain things. So try not to take it as a hit to you.
And not saying you need it, but maybe the author giving an insight into Inseo's seperation anxiety will help you understand your own.
That's how I feel when some stories hit to close to the home.
To add, the clear manipulation (ex: pretending to be sick, distracting when making plans, crying to have plans be canceled) plus the separation from friends and family, and also not letting the person out of their sight are some tactics that abusers can use to isolate victims in situations like dv. In those cases it’s less about separation anxiety and more about control, but that actions taken are extremely similar.
I think people are worried with the way it’s being portrayed in this scenario that he might be a toxic lover. I don’t think that will happen in this story, but it is definitely not a good way to handle being with a loved one. Hopefully the story is about growing and learning boundaries and respecting and trusting in them. Because for sure the way Inseo is behaving right now is not the best. I don’t see this as an attack on you or even on Inseo, but more that people are concerned or worried about Hyeok.

My separation anxiety is actually THIS bad in certain situations and the facts it's getting portrayed in here in one of the characters is amazing but the comments being super negative makes me feel as if they're attacking ME lmao anywho, I'm super excited for more of this even though for some reason, the last edit I wrote in my review was "last side story was so ass" for some reason??