I know how you feel. I also am the same, in that, I go out of my way to be a polite, well-mannered, considerate person. People are always flocking to me with their problems, and I can solve theirs fairly easily, but when it comes to my own...not the same story, unfortunately
Everyone goes through "bad patches" as it were, what you are experiencing is probably a combination of your personal problems and the **** British Summer we are having this year!
Anyway, on a more serious note. I really do sympathise that this girl cannot see how devoted to your job and mature you obviously are- I only wish there were more gentlemanly people like you around!! If she fails to understand this, which one of your major personality traits, then she fails to understand you. And if she fails to do that, maybe she's not the right one?
Whatever you do, try not to let your problems change the way you act. You'll appear a lot more dignified and generally a more pleasant person to be around, and more people will appreciate this.
You once again seem a lot like me in that you really need people's company to feel secure. I am exactly the same, I need to constantly have compnay and interact with others, but a little time out every so often won't do any harm. Go walking by yourself, it doesn;t matter where. Do something you really enjoy, eg. reading, yoga, painting etc. I usually cook when I want a bit of "me" time. This lack of "me time" may well be the root cause of your tension, which is unfortunately being vented on those close to you.
Basically, if I had this problem, and I had posted it here instead of you, how would you advise me?
-Nikki