Luo ZhouZhou was a vampire, and naturally has difficulties adapting to a weak omega body. It's really sad, and the 2 instances that were especially heartbreaking for me were the following:

In ch 38. LZZ has just been in a dangerous situation following a baddie and although he was cautious, he still kind of endangered himself. Once again, our ML Chu Feng is very worried for him, and slightly angry (even though he's also glad LZZ was more cautious than before), so LZZ says "I'm not used to being afraid of people yet. I did feel scared when I was being chased. But don't worry, I will get gradually used to being afraid of people". And that kind of broke my heart. Of course, if you're weak, you have to be cautious and careful. It's not such a big deal if you've always been weak but going from OP vampire to weak chicken omega, and having to adapt to the changes... I'm hurting for our MC.

Second is in ch 42. LZZ was once again in a dangerous situation, and handled it very well. CF meets him coincidentally right after and finds out about it, and is really worried about what could have happened to LZZ. He gently tells LZZ that while in life, people always come and go, to him, LZZ is incredibly important. He knows LZZ is brave, always fearless, but he himself isn't. He's worried, he's afraid, scared about what might happen to LZZ if one day he can't protect him. LZZ can tell how much of a toll it's taking on CF and cries, so very sad about not being a vampire anymore. Saying he doesn't want to be an omega, he wants to be a vampire again. That even being a cowardly vampire is better than being a brave omega. CF comforts him, and promises to be there for him whenever possible. LZZ finally accepts CF's concerns and his own situation, even though he's still sad about it.

As for me, that didn't only kinda break my heart. That situation must be excruciating, and I couldn't take it. It must hurt so much to fall from strength like that. So I dropped it... read the next spoiler for why I was happy I eventually picked it up again

Even though LZZ is a weak omega for most of the story, he regains his vampire strength and abilities about 85% into the novel. And he uses them in crucial situations as well. I'm very happy about that. So in case you dropped it because you couldn't take the tragedy of him having a much much weaker body than he once had, worry not.

especially towards the end when we find out more about how MC was a vampire and how it is connected with the virus. I felt like this was the biggest plot hole of the story, even though it attempts to explain what happens to MC, and how people were cured.