He cared a lot for her, definitely, though he pretended it was merely paternal love. The others, of course, could easily see right through it-- that much was obvious-- but it was easier to keep pretending he really thought it was a father's love than to actually turn around and admit it. So when he was able to do so, he would sit and simply watch her. Sometimes the others would notice and tease him for it, sometimes they wouldn't. Either way, it didn't matter, because they could never see what he really thought.
They say he's an idiot. They tease him, poke him, goad him into action. "Tono," they'd say, "your precious daughter loves us better than you!" Then it would be an exasperated, "I'm not your daughter, senpai!"
To the corner of woe he'd fly in response. He would tell himself, beflighty and dramatic, because that's what they expect. It was his way of keeping their little family together; he told himself to be their idiot "father", because a serious king simply wouldn't do-- what would happen if he took a sudden turn to propriety? He simply could not imagine what horrors the others would be struck with. He confined himself to being silly, because anything else would be dangerous and risky-- far, far too risky. Even now, he still remembered the festival incident, where he had nearly dissolved the host club, and that was definitely not an event he wished to recall. He wished to find his mother…and also to let himself move on, to let her remain with someone more deserving. Because he was the idiot who was supposed to know nothing.
But he knew. He watched, despite all his actions which clearly sang otherwise. He carefully took in how she didn't seem to be affected by anything false he did; he could see that she could see right into him, and how it seemed that her very stare was almost like a challenge. Be true to yourself, those deep caramel eyes would tell him, but he couldn't do that-- just couldn't; so each time, he'd grin widely and babble something about how cute she was, and pretend not to see the disappointment she so carefully tucked away.
If he were to be honest with himself-- and he was, just not often-- he would tell himself that yes, he was definitely in love with her. But he also knew that she probably felt nothing for him, and so he would not tell her; it would be selfish of him to do so, because it would force her to make a choice. No, he couldn't admit it.
The others might laugh and laugh and tell him it was a "defense mechanism" as though he himself didn't know he was in love-- yes, that was a logical answer, but it was wrong in that it was to defend himself. They were wrong, because it was for her. He pretended, because it protected her. It was easier to pretend not to know he was in love; it was easier to deny it outwardly. He kept up the "fatherly love" farce, and he knew that she knew he was hiding something from her. Because each day, she'd look at him, and it was plain that she was asking for him to admit it to her. He wondered if she really did know what he thought of her…
She knew. How much, he wasn't sure of, but she knew.
-----
"Tamaki-senpai."
"Ah, Haruhi!"
"What is it that you want to say?"
"…Oh! Just that my adorable daughter would look cute in that new outfit Ranka-san bought!!"
"No senpai, please--"
"Haruhi. I will always consider myself your father, so please…
…Please just leave it this way."