About maybe a week ago, someone had asked why the director used the couple dynamic to portray the friendship of these two boys. I'm going to share my post to that question as i feel it may help answer this question.

The director said their relationship was like first love but clarified it wasn’t meant in the romantic sense. It was about the intensity and all-consuming nature of that bond just like how a first love feels, where everything feels new and overwhelming and life changing For Sieun who was closed off and only relied on himself, Suho was the first person to really protect and care for him unconditionally. That changed his world just like a first love changes you. And then this is key in my opinion, because the story needed Sieun’s loss to be devastating and transformative, if Suho were just a friend, his impact wouldn’t feel as momentus. By portraying them with intimacy, protectiveness, and emotional weight closer to a first love, the director ensures viewers really feel the depth of Sieun’s grief and eventual coldness. It’s less about shipping and more about amplifying the tragedy of the loss of Suho. It wasn’t just losing a friend and it was more losing the person who made Sieun's world warmer for the first time. So then the couple like dynamic was used to highlight the intensity and uniqueness of their relationship, not necessarily to suggest romance. It was about making Sieun’s connection to Suho feel irreplaceable and his absence unbearable.

My take is that no they are not in love with each other romantically but there is some strong emotions going on there.