Advice and ten easy points?

In a relationship, isn't it necessary to be able to communicate honestly and respectfully your needs and tell honestly how you are feeling? I follow all the standard rules of good communication (listening, empathy, compromise etc.) but if I broach an issue with my gf, she gets very defensive and tells me she doesn't know how much more she can take. This makes me feel guilty and scared of expressing myself in way that might contradict her even though I don't mind if I don't get what I wanted, it's the feeling of being listened to and understood that I want and compromise isn't a problem. She thinks I am a bad bf becasue of this. What can I do?