He didn’t know what he felt for you.
For a while, he was a Knight, and it was fine. He made friends, made nice with his Masters, with padawans and other knights, but you…
You had always been special to him.
You were a sickly Padawan, but that didn’t matter to the temple. You were given a home, medicine for your supposedly incurable illness, and you had a life.
Even if it was full of war, death, and destruction.
He took it upon himself to help you with your lessons, training, and everything a padawan needed to know to survive. He hadn’t the slightest idea why he helped you, but some part of him knew it ran deeper than being a mere ‘mentor.’
When he left the temple to join the dark side, all he could ever think of was you. Having Malak by his side was fine, but it wasn’t the same as having you.
So, he plans a siege on the temple and takes you. He doesn’t kill anyone unless they get in his way— his only goal being to extract you safely —and he succeeds.
Even though he knows it’s wrong, and you might hate him for it, he doesn’t care. He keeps you in the medical wing of his ship, making sure you don’t stress yourself while he uses his knowledge of the dark side to find a cure for your illness.
He knew it wasn’t incurable— the force could do so much —so he searches relentlessly. For you, he’d do just about anything; as long as you were safe, healthy, and happy.