Been with my wife for 4 years, been married for 3 and have lived apart for the majority of that time (i.e. when not on leave). During this time I've completed 2 tours of Afghanistan and spent time away on UK and other overseas tasks, training, etc. It can be very difficult, especially if you are used to living in each others pockets at the moment. We make it work by making the most of our time together so at the moment that includes the weekends and any leave we have. We tend to go 'all out' on things such as nights out, holidays, etc. I once had to break the news that I was being deployed for 4 months with a couple of days to spare; as you can imagine, that went down like a tonne of bricks..! Cases of things such as that are extremely uncommon but you have to expect the unexpected and go with the flow. An open mind and some flexibility goes a long way..!
If this sounds rather negative then I must emphasise that the RAF has given both me and my wife some great opportunities in life. A decent wage and leave allowance that means we can go on nice holidays, we have had help buying our first home (which we are soon to rent out, meaning somebody lease will be paying our mortgage), the chance to visit a wide range of places that very few people do (we have met the Queen at Buck Palace), and the chance to visit different parts of the country and broaden our horizons (one of my previous tours involved having an all expenses paid flat in Central London - we made the most of it, theatre, nights out, sights, etc.).
Fortunately we will soon be living together on a permanent basis which will be great (I hope..!). At the moment we speak in work and exchange emails a few times a day. Depending on his trade your boyfriend should be able to keep in touch fairly easily. Training is a different situation, but it doesn't last forever and soon it will be as if he has a 'normal' job.
He will be focused on his training at the moment; all I would say is stick with it, appreciate that he is probably under quite a bit of pressure at the moment, and try to be supportive. Perhaps find out about his graduation and make plans for attending that. Or arrange to go down one weekend (when he has a free one) and have a night in London.