Long distance

Met my bf in the RAF so have been doing the LDR!

The main thing is trying to plan when to talk and meet up, and both accepting that it won't always happen. You will both have times when you are tired, busy, stressed, your gf with assignments and exams, you with keeping on top of training with kit, lack of sleep, a lot of physical stuff. Neither of you may feel like talking or may get snippy with each other, so just call a time-out and talk another time. Exercises and some operations can have restrictions on personal communications too.

Uni and the RAF are also both great opportunities to get involved in additional activities, for your gf things to put on her CV, for you for promotion, and both of you for doing things you already enjoy or want to try new; these could be at weekends or after hours. Time off during Phase 1 training is limited, specialist training is more relaxed, with weekends usually free. Once in your job, you could be working 8-5 Mon-Fri, or doing shifts. You will also have extra duties, depending on what you are joining as, eg guard duty, parades. Leave will be as the job allows. Again, accept that you won't always be able to talk or get together when you want. You will be able to visit each other and your gf stop with you on base, so it's a chance for her to see what you are doing.

Finally, depending on what role you are going for, you could move jobs every 2-3 years as an officer, less frequently in other ranks. With some jobs there are a lot of bases that you could get posted to, some there are very few and you can ask for, but won't necessarily get your choice of posting.

Talk to your gf and make sure she understands what the military entails. Also, have a look on the Armed Forces Forum as this kind of question has been asked a lot on there, though usually by the person not joining up. I think it's great that you are considering the both of you, and good luck.