A fight from nothing with my gf becoming brutal?

Okay. My girlfriend and I, we've been together since 2/14/2011. We have basically went through a lot before hand, and decided to get together one last time. We fell in love, realizing we were the only people to make each other happy. We go through a lot of stuff, a lot of fights, a lot of mushy tears of joy-like moments, just things serious couples go through. One of the times, I actually got caught with porn on my itouch.. Ever since that happened, she definitely doesn't trust me 100% like she used to. But we got over that rough patch, and we were back in business for a good long time. Skip forward to now, lately I have been hostile to her, not physically, just verbally. I'm very impatient with her now and I'm usually a jerk when my fuse goes out. But here's what happened. Tonight, on facebook, on a like page, I shared a picture that basically said that people will text emoticons but not have the face in real life. Then I looked on that page, and commented on one of the photos where it's a slutty looking girl posing and a guy usually making a scary face in the background. I commented on the photo, "brix shat." My girlfriend messages me, saying that "I don't mean all the faces that I always text to her, and that I was checking out the girl in the picture." I tried to explain to her that I found the text picture humorous and I wasn't staring at the girl. She says I was. So then, I said "I'm not going to argue about this. But I know what is true..." And before I got her even more mad, I thought I would try to fit a lyric from a song in there, "YOU ARE THE LEGEND, THE LEGEND IS TRUE." She then goes on about how I don't take our relationship seriously, that when she is trying to talk things out with me, I am just goofing around and try to avoid it. I just wanted to make her smile, I told her. But she said I'm not paying attention. I told her, "You're right." So we pause for 20 minutes. I don't say anything, I just thought I would let her blow off some steam without making the situation worse. Then I tell her, I am ready to start talking things out. What does she say back? "I don't want to fucking talk to you right now.." So I tell her, "Okay, you don't want to talk to me. Just call me when you want to talk this out. I'm getting off facebook." She says "No. YOU call me when YOU need me." I tell her, "Well I may as well call you right now... I need you baby.." And then she says "I don't fucking want to talk to you right now.." So I tell her, "Okay then. I'll call you later, love you. Bye.." Then she says back minutes later(I find this message an hour later after a building session on minecraft to blow off steam,) "fuck you..." I was shocked. She has never, not once, EVER told me fuck you before, at least in a serious manner. So I go on here to type this, and she calls me. We talk on the phone for a little bit, I apologize to her, tell her she's beautiful, and that I love her, and things seemed fine. But I still just don't feel right about this. Usually our fights end with tear filled "i love you baby I'm never going to leave your side" moments, but instead she just said "it's okay babe," and fell asleep on the phone, like her cute self always does. I honestly feel dissatisfied with what we have right now, and I cry looking back at the good times before the itouch indecent. So I posted this to mainly ask, who's right, who's wrong, who do you guys think should break up with who, or if we should stay together(I want to stay with her as long as I can, I can't live without her..) Thank you for reading this...