Based on the phrasing "exclusive," you are likely looking for the specific manhwa (Korean comic) that fits this description.

The Power Imbalance:

Real love requires a level playing field. In this dynamic, the "exclusive" nature of the crush is built on an inherent imbalance of power and life experience. How to Handle These Feelings

The Review

The story typically follows a young protagonist—often a student or a tutor—who discovers a hidden side of his friend’s mother. The narrative centers on their forbidden relationship, complicated by the protagonist's loyalty to his friend and the societal taboos surrounding the age gap and familial ties.

We hear countless stories about first love. The sweaty palms in the school hallway. The passed notes in calculus class. The awkward slow dance at the homecoming assembly. But what happens when the object of your first, most consuming, and most confusing affection isn't the girl in the next desk? What happens when she’s older, wiser, off-limits in a way that no high school crush ever could be—because she happens to be your best friend’s mother?

Everyone who has whispered "my first love is my friends mom" knows this timeline by heart.

I realized then that "first love" isn't always about the person you end up with. Sometimes, it’s a lesson in boundaries and the painful realization that you can’t always have what you want without breaking something precious in the process.