My ex-girlfriend suffered from severe anxiety disorder.
Anxiety can be very debilitating. 
It was. She would often have significant feelings of anxiety and fear. It really was the cause of the breakdown in our relationship.
That's too bad. The fear can be quite often very hard to overcome even if it seems to be irrational
It was. She was inclined towards socal inhibition and would have difficulty holding down a job or even leaving the house because she wanted to avoid social situations.
So it may have been a touch of agoraphobia as well?
Perhaps she suffered from the early stages of agoraphobia. She was really more bothered by social situations, but did begin to associate that with places by themselves.
For an introvert suffering from anxiety crowds often trigger panic attacks.