i may suggest the same thing a lot, but really, i believe people should talk to each other and be honest. there's no better way to clear things. do you think you can talk to him like that? perhaps mention how sad you are that now that you got a nice opportunity for your career, it would have to be far from where he is, or ask how he feels about anything he's going through, say that you've been thinking how tired he may be after training for that marathon and you feel like doing something for him to enjoy, like preparing your night together (choosing your dinner and plans like a movie) and giving him a massage. what do you think of that?
don't let yourself think too much, specially if you're thinking by yourself while you are not able to talk to him. try to send him a message during the day, to let him know you're thinking of him. my girlfriend taught me that, little things count a lot, i'd say she even spoiled me haha and it's great.
hope my opinion helps, and remember to never let yourself overthink those things, the best way is always try to understand each other alright?