This is a whine/moan. Have you found yourself in this situation as a writer? You've invented a character whose role is to create problems for your MC and make it more difficult for him or her to achieve his or her ultimate goal. This character isn't exactly an antagonist, he may even think he has the MC's best interests at heart, but before he's done there's going to be a conflict and the MC will be set back in some way. So the problem: You're writing this character, and he/she is turning out so damn attractive you don't want to write the scene where the crisis with the MC comes. But you have to do it to forward your plot and you've written the character such that the crisis is inevitable sometime. Woe! Agony! Lament! Moan!
It's called an Obstacle character. He or she may be sided with the antagonist, but not always. They may even be on the side of the protagonist, but simply make it hard for him/her, such as a buffoon or someone who constantly tests the character to make them think deeper about what they want/need.
Or eventually write a separate spin-off story where that character is the MC and deals with a future situation based on the previous conflict with the previous MC? In the current WIR, he's got to be likable so the protag. will be all the more devastated when she uncovers out his intolerable flaw.
