Maybe just show him your concern and that you are asking because you're his wife and love him very much. And that you are there when he is ready to talk. Keep it short and simple. Just show that you understand he may be going through something, but that you are there for support.
thank you very much. that is the jist of the note i sent h yesterday. it was handwritten on a nice plain cream colored note card, not anything flowry. i mailed it and he should get it today. i told him that i miss talking to him and the close friendship that we enjoyed as part of our extrordinary marriage. and that i am here when he is ready to share anything about what has been troubling him. that my feelings for him are strong and i am still his soft place to fall if he so chooses.