The extra goodies had been at Henry's insistence. He knew his son did okay with the food on campus, but they didn't have anything that compared with a dozen fresh hum bau—and besides, steamed pork buns could easily be reheated in the microwave in Marty's dorm room. (10.1)
Henry may have a hard time sharing his feelings with Marty, but he shows his love for his son in other ways. He buys him extra food to take back to the dorm and always makes sure that his bills are paid.
She shone like a light. "I'm Samantha, I've been dying to meet you." She stepped past his hand and threw her arms around him. Henry patted her, trying to breathe, then gave in and hugged her back. Looking over her shoulder—smiling—Henry gave Marty a thumbs-up. (18.43)
When Henry meets Marty's fiancé for the first time, he makes a point of being friendly and accepting even though she's not Chinese. Henry doesn't care about her race; he just wants her to love his son completely.
"It just came out. I saved up to buy it. For you."
"For us," Henry corrected. "Besides, I can't even play it, we don't even have a record player."
"Then come to my house. My parents want to meet you anyway." (24.27-29)
Keiko obviously cares about Henry if she'll save up all her money to buy him the Oscar Holden record—a record she doesn't even own herself. And Henry cares about her enough to tell her to keep it at her house so they can share the precious recording.
"Did Mom know about all this?"
Henry felt the Ethel-shaped hole in his heart grow a little emptier, a little colder. He missed her terribly. "A little. But when I married your mother, I never looked back." (29.25-26)
The fact that Keiko was Henry's first love doesn't mean he loved Ethel any less. After he married Ethel, he was completely devoted to her—and he still misses his wife every day.
Henry had thought about Keiko off and on through the years—from a longing, to a quiet, somber acceptance, to sincerely wishing her the best, that she might be happy. That was when he realized that he did love her. More than what he'd felt all those years ago. He loved her enough to let her go—to not go dredging up the past. (33.23)
The fact that Henry hasn't sought out Keiko after all these years doesn't mean he gave up on loving her; he just loved her enough to let her move on and live out her own life.
After a few days, his mother did acknowledge his existence, in her own way. She did his laundry and packed him a lunch. But she did it with little ceremony, presumably so as to not go against the wishes of Henry's father, who had followed up on his threat to disown him figuratively, if not literally. (36.3)
Henry's mother doesn't stop loving her son when he's "disowned" by his father. Instead she finds little, invisible ways to take care of Henry. She still makes him lunch and does his laundry, though she doesn't talk to him directly.
His mother knew, somehow she knew. Maybe it was the loss of appetite; mothers notice those things. The distracted longing. Feelings can only be hidden so long from those who really pay attention… All because of you, he thought. I wish I could think of something else—someone else—but I can't. Is this what love feels like? (36.53)
Although Henry doesn't talk about real emotional topics with his parents, his mother still knows what's up with him. She can see that he's fallen in love with a girl for the first time, and that it's doing a number on him.
Their good-bye had been a formal one. After he'd decided to let her go (for her own good, he reminded himself), he'd kept a polite distance, not wanting to make it harder on either of them. She was his best friend. More than a friend, really. Much more. The thought of her leaving was killing him, but the thought of telling her how he really felt and then watching her go, that was more than his small heart could manage. (38.4)
It's heartbreaking for Henry to watch the girl that he loves—the first girl he's ever loved—walk away from him. But what can he possibly do? He's just a kid; he can't stand up to the whole U.S. government.
"Good morning, Henry. How's it feel to be a prisoner for a day?"
Henry looked at Keiko. "Best day of my life."
Keiko found her smile all over again. (41.28-30)
Henry loves Keiko so much that even being in a prison camp seems better than being at home with his parents—as long as he gets to be with her. He doesn't care about anything else; he wants to spend time with the girl he loves.
I love her. Henry paused at the thought. He didn't even know what that was, or what it meant, but he felt it, burning in his chest—feeling fuzzy inside. Nothing else seemed to matter. Not the somber crowd of camp workers drifting to the barbed-wire gate. Not the machine guns in the towers above. (42.22)
When Henry leaves Keiko at the camp, he realizes that his heart is full of some pretty heavy feelings for a young boy—but he just rolls with them. There's nothing that can dampen his spirits now that he's in love and knows his feelings are reciprocated.