He isn't (that) stupid. A part of his mind is actively refusing to let him see what EVERYONE else in the story can see. So yes, he is cockblocking himself. And Takagi-san sees that too. Maybe she knows how it's going to end, so she's in no hurry.
So why does he refuse to see? Fear of her? Fear of himself? Fear of the unknown? Issues with parents? Religious guilt? Alien parasites controlling his brain? ??♂️
If you think about it, it makes sense he's afraid. Would you want to be in love with someone who can read your mind?