"Luke..." he started when the other Skywalker opened the door. But he really had no idea what he was supposed to say in a situation like this. Obi-Wan was better equipped for dealing with angsty Skywalkers. But Anakin had wanted to be here for Luke. He knew that the time Luke was from, Anakin hadn't been there for him. He had turned to the Dark Side at the time Luke was born, so Luke and Leia had been hidden from him.
But he was here now, and so was Luke. Things could be different in Storybrooke, things didn't have to end up the way they had at home. And Luke was distraught at the moment. Therefore, Anakin wanted to be there for the slightly younger man.
"I thought you shouldn't be alone. Losing someone..." Well, it hadn't worked out to well for Anakin, had it? "It can make you do drastic things." To say the least.