Quote 4
"Declarations of love amuse me, especially when unrequited." (3.57)
Jace's amusement at unrequited love is ironic because he has his own unrequited love for Clary, his sister. He'll get down off his cynical high horse soon enough.
Quote 5
"Falcons are not meant to be loving pets: They are fierce and wild, savage and cruel. This bird was not tamed; it was broken." (11.160)
This story told by Jace says a lot about why he puts up a prickly façade to keep people away. He's both scared of loving and being loved. Vampires on the other hand? Not scary at all.
Quote 6
"My oath to the Covenant binds me," [Jace] said. "No such oath binds you." (8.60)
Here, Jace is telling Clary that she can tell Simon all about the Clave, etc., because she isn't forbidden to do so. We have a feeling that Jace wouldn't tell Simon anything even if he had a gun pointed at his head. There are some rules you just don't break.