Ok, thanks for explaining why you personally feel that. Now, let me respond with how I feel about your points.
1) MC has a habit of keeping secrets. He does, but because he wants to be the hero and protect the girls from everything. Maybe it might be better in some cases if he did tell them, but he has already lost his parents, so it has given him a complex of trying to save everyone and not worry them. He takes on all the problems by himself. Everybody has flaws and that certainly is a flaw for him.
2) Why does he lie about taking the serum? It's explained in the story. He was bit by the Beast, and that has increased his need for blood as a vampire, so in his mind, that can only mean he is more like the Beast and he scared of turning into that, even though it makes him physically weaker. BUT now that the Breast is back, he's willing to risk that to protect the girls. Especially because he doesn't know if his parents were targeted or if the Beast will come after the girls next.
3) He's emotionless. Really? I think he has shown a lot of emotion and turmoil. Every single time the Beast gets brought up, she even has a emotional reaction to it, so I'm not really sure why you feel that way. Even in the latest update, there was a lot of emotion at his mother's funeral, and he had a panic attack just thinking about the Beast's attack when he was a child in this latest update.
Of course I'm a bit bias since I write the story lol. But I hope I explained why everything is the way it is