Right OP, it is crystal clear, and backed up by a lot of your threads, that you have an insecurity issue. Insecurity is normal in a relationship and, in my experience, it can increase when one goes to university. But I need to be clear, if you keep questioning her and making her feel untrustworthy, she WILL begin to resent the relationship and possibly END it if she feels she has to constantly tip-toe around you all of the time due to the fear of being unnecessarily held to account.
You seem to think that every guy is better than you and your reasons for this are always to do with physical things. Your girlfriend picked you in the first place when she could have picked a load of different guys, why are you so worried? Trust me, I've been in your situation and I know how you feel. But there comes a time when you have to deal with your problems YOURSELF rather than seeking constant reassurance from your girlfriend or on TSR. I'm not criticising you, I generally want to help. But you have to be more confident with yourself. You need to do your own thing and be your own person for a while without resting your life on your girlfriend. You seriously need to take some space I think, and give her a little too, it may help.
By doing your own thing and improving some of your insecurities you can increase your self worth, which will have a positive effect on your relationship and the way your girlfriend feels about you (Not saying she feels negatively towards you, but she may start to if you continue to have no confidence). I used to do similar things with my girlfriend and was also insecure. One day I just decided to put myself first and deal with my problems. You have to trust her and realise that you're neglecting yourself by CHOOSING to feel like **** all of the time. You may say it's not a choice BUT IT IS!
Only you can choose to say '**** it, I need to stop thinking of what is going to happen in the future and focus on my life now'. What is dwelling on all this negativity going to achieve? NOTHING! So start doing things to deal with your problems rather than feeling sorry for yourself all of the time. Things will get better only if you choose to make them better.
Good luck.