Don't you think this manga is way too exaggerating the consequences of lying...

I'm pretty sure that if the main character knew how to PROPERLY lie he would end in a much better situation than if he were to tell the true. From time to time i come to the conclusion that he have brain damage because of the things he says...
Like for example

For the Agatsuma thing something amount the lines of "If i tell you i'm gonna have to kill you, and if you open your mouth we would know i promise", or if he wanted to say the true but keep it short, something like "My organisation is going to clean your memory if you keep on getting your nose into this, i'm not kidding, if you ask your friends what happen at school, they won't remember a thing" or if he wanted to keep the alien bull crap "I have imnunity to the alien virus, but you might die if you get to close to them"
This are just examples, but i just found annoying how much the mangaka tries to make lies bad, offcourse things would go terrible wrong is the best lie you can come up with is crap like that :S^

You can't live your life telling the true to everybody, people hate the true
also, what with all the " Lie " thing?

It's not about lying, it's about not opening yourself to others and never trusting anyone. The protagonist didn't simply fail at lying, he utterly failed at any communication and his way of doing things only made his own life harder.