Why haven't you talked to him about it? At this point your relationship is likely to suffer through lack of communication and lack of interest in his career. He can give more info to you because he can say where he is training, how long for, where he could be based in the future.
Communication will be difficult or restricted during the first phase of training, but more relaxed with free weekends for the next stage. After that, it depends on his job, but he will get extra duties even in the UK, such as security and parades, as well as other courses to improve his skills and progress his career. There will also be the opportunity for him to be involved with sports, adventure training and social events, some of which you could attend. You can also see about visiting him when he's more settled.
Bit different for me personally as my boyfriend and I are both ex-RAF, met whilst serving. We were in separate roles which took us to very different locations and had a year apart across 1000s of miles and various time zones where the comms weren't always great. As you say, mixed reviews. I've seen couples across all ages and some manage it, sone don't. Plenty of partners become the stable point, living off-base and having their own career to keep them occupied.
It takes commitment and patient, and acceptance when he's tired, busy, unable to discuss what he's been doing. Sit him down ASAP and start talking!