The 'lover boy manhwa side story' could potentially explore different aspects of the love interests in the main story. It might show some of their past experiences that shaped who they are in the main narrative. Maybe it delves deeper into their personalities and how they interact with the main character on a more personal level outside of the main events of the manhwa.
Well, you could try doing things he likes together to strengthen the bond. Also, showing appreciation and support for him can go a long way. Sometimes, small gestures of love and care can make a big difference.
One way could be to have heart-to-heart conversations regularly, listen to his perspective, and work on resolving any conflicts together. Surprising him with small gestures of love and support might also make a difference.
Well, the side stories in this manhwa might show what happened before or after the main events, or give more insight into the characters' thoughts and feelings that weren't fully explored in the main story.
It could be that the story hasn't developed enough to bring those people into your character's life. Or perhaps your character has trust issues preventing others from getting close.