This sort of career can be a great opportunity, my DP has seen the world, earns a decent wage and has a job he enjoys.
BUT your relationship needs to have a very solid foundation of trust. Lots of time away, nights out drinking with the lads, 'rig runs' (going out in uniform) staying on the same corridors as female recruits etc are common place.
For some couples is works, for some it doesn't. Wishing you luck!
After initial training, expect him to be away a lot for at least the first couple of years, depending on what specialisation he is, and potentially his whole career. You're not supposed to be away more than 660 days in any rolling 3 year period but a fair few people are breaching that at the moment. The trade-off is pretty good pay and allowances, especially when away, long leave periods (basic of 30 days per year, plus 8 bank holidays, plus another day for every month he is deployed and more if he's on an operational posting), good professional training (varies between trades though) and a great life for him. There's not often a lot of scope to take leave when he or you want him to though, as it tends to depend on when his unit grants it. Usual routine involves 2 weeks at Christmas, 2 at Easter and 3 in the summer but this can be VERY variable depending on deployments, courses, what specialisation you are etc etc.
He's going to the recruitment office next week to talk to them but I'm just curious as to what me and the DCs can expect. Will he be away a lot? Leave etc? I have no knowledge of anything like this and although I'm supporting DP I am also slightly worried.