As you were told you did not have an exposure.
you had no risk and you can have unprotected sex with your GF.
So should i not have to worry anymore? Do i need to test for HIV & STD? Can I have sex with my girlfriend again after my silly incident?
There is no way possible to take a condom off and put it back on without being exposed to air or any of the other obstacles.
Last question hopefully.. So is it applied too if the semen was in intact condition inside the condom, not expose to the air & accidentally i'm wearing it?
HIV is a fragile virus and does not stay active outside it's host. Once exposed to air, PH change and/or temperature change it becomes inactive.