No. Though he is 'more like little brother' but their big brother- little brother dynamic turn into boyfriends after they made out. Mc is growing and being more mature slowly but mostly, ml stopped being 'overprotective' and he actually starts to show his desires openly.
Small spoiler
When they have sex, i think they both enjoy the idea of 'they are stepbrothers'. The thing that seaparated us at the beginning turns into dirty sex talk. 'Do you like doings these things with gege'.
If you ask me, their dynamic is pretty much like most bl couples. Innocent puppy bottom relying on cold-hot top so if you are worried about grooming, there is none. That is why its slow burn romance because mc had to grow and realize his feelings on his own.
They aren't step siblings. Lele is a legally adopted as a "Foster child". Lele explained it himself, that She ng Yu's parents didn't want to legally adopted him as their son cuz they didn't want to take away Lele's parents place in his life. The Songs are legally his Foster Family. Step siblings and foster siblings are two entirely different things.

Can someone give me a quick summary? Is this worth reading?