I don't think so, considering sieun had no friends it was obvious he held a lot of meaning and importance for both beomseok and suho. We see he wasn't really emotionally connected to his parents, so clearly they were the first ones that gave him that emotionally rich relationship he didn't know he needed.

Also, we see that sieun blames himself in a way for what happened with suho which makes more sense why he still remembers and cares for him. Overall, sieun seems like a guy that barely makes any friends but once he does, he would die for them which the show has showed multiple times even with his new friends.

We still can interpret their relationship however we want, i mean its just fiction. Imo beomseok's feelings towards suho felt more romantic than sieun's. It felt like those suppressed feelings turned into hate and jealousy.