Why does the narrator decide not to pursue Liza?

I read this so long ago. A I recall, the Underground man is pretty self -absorbed. He really doesn't know why he berates her or befriends her; he just does things.He also has gotten used to pain and suffering, it's as if he wants to spread this same suffering like a virus. Some critics think he is in love with Liza. Suffering is this guy's world so why not suffer together. That's pretty romantic! In any case, he keeps Liza away from him: unable or unwilling to connect with her.