My H and I met while we were both working in SE Asian country. That place became very very special to us. The situ that lead up to his A was that he changed job due to layoff, and went to a European venue. Okay so different than your situ in that you both are going to Brit venue together, but I wanted to share this about what I saw as a trigger for stresses that lead the way to A's:
The expat community that you may associate with is colourfull and interesting -- but the community is also populated by an amazing number of a$$holes who are living the life and doing the dirty because there is a culture of "geographical separation" which is celebrated and used as an excuse to cheat ( and UN and NGO people, I am *so* looking at you when I say this ).
I'm not exaggerating this; I have seen this for years, watched my friends suffer in their own relationships when they were hit by it, and now am here because my M got hit by it.
Yes, have friends among the expat community but fine tune your radar, because there will be predators who are exceptionally well versed in the art of "friends with benefits" and offers of a shoulder to cry on if culture shock affects former WS. You both will be experiencing big big changes with living situ and career changes -- so recognise that THIS is the time when you especially have to lean in to each other, and that comfort from *any* outside source just isn't acceptable in your R.
Having said all this, I also want to congratulate you both to be making big changes, and my fondest wish is that this is a blank canvas for your R. Be excited, savour the experience, and love each other like you are each the only person the other has -- which is true.