RAF?!? eww. All jokes aside yes all military basic means you rarely have contact with your loved ones. I do believe you get holidays like Christmas off for a few days. All I can say is that offer him your full support. Training is hard and very intimidating and he will appreciate the support you give him.
I am not suggesting breaking up or anything like that I am not in a position to do so nor is it a good idea, but my girlfriend broke up with me because of military complications and it didn't go too well for me. It will be hard don't get me wrong, so I would really do some research to prepare yourself so your not surprised in any way and end up doing something that damages his future.
Before I broke up with my girlfriend I was abroad and met a US couple in which the husband was a WSOP in the air force, I asked them how was the relationship was during his time in the military, the response was: "it was hard but you get used to it and it was worth it."
All the blokes I was with who had girlfriends I was jealous of, they had someone to talk to, impress and relax to despite the lack of time they got together. During that time your support will be priceless to him.