Well, anger in response to a threat is probably just an offshoot of my sympathetic nervous system reaction - increase heart rate, breathing, etc.
i wouldn't say it's a reaction 100% of the time.
seuqence of events 1. I attached a meaning to her not saying IlY back. 2. the meaning is clearly that she doesn't love me (now I know this is irrational) 3. When I don't get that reassurance I have a physical reaction. 4. Sometimes that evolves into anger - partially at myself and her.
Anger probably allows me to harness something inside that othe reactions can't.
Patience is bitter, but its fruit is sweet. --Jean Jacques Rousseau.