Advice very much needed?

oki im 17 years old and im going to germany next month alone(to see my girlfriend of a little over 2 years) but this is the first time ive had to leave the country to see her,she lived here for 2 years but she returned home after highschool..the longest flight ive ever been on is like a hour long flight and this one im about to take is 8-9 hours long any tips on air travel??