Hrm. Well... You could sit and think out what YOU might need to weather the storm even if it is happening in "another country." Then you could ASK him if these things can reasonably be provided by him.
I am hearing something like...
"I want to give your privacy and space if/when you are having issues in your marriage/primary relationship. I am willing to step back to give you the room you may need for emotional management on that tier of the polyship.
However after X days, could I please get a (text/phone/call/something) to reassure me that you haven't forgotten I'm here in the wings? I don't need to know your private business, but it makes me worry when you are out of touch for a while. Even just "Hi. Still working on things here. But I do think of you and miss you!"
Maybe you could tell him something like that.
Some care and concern for YOUR well being too as a secondary. Some acknowledgement/grateful for your willingness to step back and how you are trying to be an agreeable/easy-to-get-along with type poly partner. Not all up in their biz, but you know... Just a "Hey, thanks for that. I appreciate you" doesn't hurt.