Hi,
Firstly I assume you've had a chance to speak to your boyfriend then?
Rejoin times can vary and I'm sure someone else will be able to give solid timeframes for that.
With regards to him leaving and rejoining, I don't pretend to know what situation you're in, but what I can say is that situation isn't likely to change. Its obviously not ideal that he is in training now, however if he/you both has plans to rejoin later then chances are that wont be an ideal time either.
What I know for fact is, he'll be in a job which provides a good wage for a young lad which increases every year and provides extra allowances when away. It may also be able to put a request in for married accomodation. Often lads who aren't married but have kids with a long term partner may be able to get a house on the patch if there are some available. What I'm trying to say is, although at the minute it seems like worse scenario having him away, long term if you're planning on starting a family it may be a really good stable job for him to be able to support you.
Whenever faced with tough choices my mantra is always "dont react with emotion, respond with logic" . Trust me, I know that's easier said than done but have a long think before your fella makes any impulsive decisions he may regret later on.
Apologies if my advice is rubbish, but I do sympathise with you and I hope you and your boyfriend are able to figure it out.