I do the wrong things, how do I do what's right?

I feel really stupid. I can never say the right thing and somehow manage to upset the people I care for the most. I don't know what to do, I'm so confused. How do I do and say the right things when all I can do is get so frusterated that I do the wrong things and say the wrong things. I don't even do it on purpose, I can't think when my gf and I are fighting and I always manage to upset her worse when all I really want to do is talk to her, and try to make the situation as easy as possible instead of hurting each others feelings.

So, how do I do the right things? Thinking isn't going to work because I'm already dumb as it is because I say the first thing that comes to mind and when she says she doesn't want to talk to me right now it makes me really upset to the point where I want to start beating myself in the face, but I keep asking and asking hoping she will open up to me then after a few minutes of it I get so pissed that I say wrong things. I hope you understand what I'm saying....

So pretty much,

Why do I do the wrong things?

How can I make her open up to me?

How do I do what is the right thing?