<human>: Condense the text into a few key points

Hey guys, something recently happened to me where I need to find answers. I (24 year old male) have been with my girlfriend (25 years old) for 4 months now, I truly love her and would do anything to make her happy. After I visited her at work earlier tonight we were sitting in her car and she looked upset, so I asked her what was wrong. She told me she wasn't happy with the way things were going between us, and the major contributing factor is how I can be emotionally distant at times such as when she wants to talk about sensitive subjects (such as exes, work, the future) I tend to shift the conversation to something else or just say that I don't feel like talking about it. 

This is devastating and also disturbing for me to hear, since the last girl I dated (it was for 2 months but we weren't official) told me the same thing, that I was emotionally distant and unwilling to open up. My girlfriend is going on vacation for 4 days with her family (from this sunday to next wednesday) and she told me that she is going to take that time to think about our whole relationship and she wants to make sure she doesn't make a wrong decision. She has told me this before, that I need to open up to her but I guess I never did, and now this is hitting me like a ton of bricks. 

I plan on seeing a therapist soon to try to talk about this issue, since I act this way around others too, such as family members and friends. The fact of the matter is that deep down, I am a good person, and I am willing to do whatever it takes to make her happy and also for our relationship to work. What steps do you guys recommend I take to show her that I am really willing to change? I appreciate anyone who takes the time to read this.
<bot>: What can I do to show my girlfriend that I am ready to open myself up emotionally and to break these walls down that I put up from being hurt once before?