Sulf-fulfilling prophecies. Don’t bring up obstacles that just aren’t there. If everything is going well in theory, then there is no problem, and there will be no problem as long as you don't bring up issues that are purely imagined by your mind, molded merely by your sense of fear and insecurity. Let her actions and her words speak, through time; let them dissipate any doubt you may have... Confidence and happiness are what makes a relationship strong, and confidence and happiness are what will make her love you and want to be with you for a long time.
You can't change your core, I know, but you CAN improve your behavior towards people. And I think when you learn to love someone, I mean, once you understand what it is to truly love and respect someone, you will want to be a better person automatically, you will want to be someone you love, because you want them to respect you. Tell yourself that whenever you shout at someone over futilities, you are losing a bit of their love and respect. Whenever you are being jealous of other people, you are telling her that every one else is better than you, so losing a bit of her love and respect again. The more you show her signs that you are unworthy and not good enough, the more she will believe it herself. Now tell yourself that this person has been honest and caring and patient with you, but that she will not be like that forever and you know she doesn't have to keep up with it if it's causing her pain and tiring her out...
So yeah, change for the better, if that's what you want. Improvement is always possible, especially if you're that willing.
And if some day this relationship doesn't work out because of your personal issues, you know what, let it be a chance for you in the future to possibly be with someone who is much better suited for you, someone who will need you as much as you need them, someone who doesn't drool over celebs if that's something that ticks you off, someone who will give more attention to you than to other people in their entourage because that's how devoted they want to be to their partner. This girl might be amazing, honest, caring and all, but, maybe she doesn't really understand the needs of a person like you.
Whatever happens, good luck and, honestly, I think your first step towards improvement and a state of mental peace, is to take a break from social media. What you see online is obviously driving you insane... Stop doing that to yourself. (Social Media Depression: [url=http://health.howstuffworks.com/mental-health/depression/questions/social-media-depression.htm]HowStuffWorks "What's social media depression -- and might I have it?"[/url])