I am ex RN and not aircrew, but have known a lot over the years - some of you are quite pleasant
so please excuse a different perspective.
1. However much you explain to your significant other in advance about what it is going to be like, they don't understand it until the day it becomes a problem to them. Then it becomes a problem to you.
2. This is especially an issue if they are a professional & don't have a relocatable career. Nurse is better than brain surgeon; primary school teacher is better than university lecturer; part-time anything or nothing or parent is ideal. It is not a value judgement, just a reflection of the realities of the job market.
3. BUT if you decide to leave the services and stay with the girl then you could end up dealing with exactly the same issues outside. I once moved 7 times in 7 years (countries that is), all in civilian life, and in my case parting company with my wife en route due in part to dual career professional stress. Wrecking a marriage and two careers is not ideal, perhaps better to make better girlfriend selections early on, if you are likely to be in a mobile career. In this respect the UK armed forces' posting options are generally better matches for spouses than some civilian options.
Good luck, pp