The magic lies in contextualizing their possessiveness as a symptom, not the sickness. If the male lead's overprotectiveness stems from a past trauma—maybe a previous partner's betrayal, or losing someone dear—it reframes his actions as a flawed coping mechanism rather than innate toxicity. Readers see him wrestling with his own impulses, which is key.
I'm thinking of novels where the guy catches himself being overly jealous and hates that part of him. That internal conflict is everything. His actions aren't painted as romantic, but the narrative makes you understand the root cause. The story might balance it by showing his deep, unwavering care in other areas, like quietly supporting her career ambitions or being her safe haven from external threats, making the possessiveness feel like a single, albeit loud, facet of a complex loyalty.
The 'without villainizing' part hinges on narrative empathy and consequence. He should face realistic pushback from the female lead and experience growth; stagnation turns him into a red flag. The reader's sympathy stays because they're invested in his struggle to be better, not just his desire to have her.