In the manga, Mikasa's story doesn't have a traditional romantic ending. Her relationship with others is complex and not centered around a romantic partner. She's primarily driven by her loyalty and duty towards Eren and her comrades.
Mikasa loves Eren without a doubt. This is evident in various scenes and her constant concern and protectiveness towards him. It's a key aspect of their relationship in the manga.
Yes. This event occurs as a significant plot development and has a major impact on the story. Mikasa's action is driven by complex emotions and circumstances within the narrative.