Distance, nationality, religions etc might be creating insecurities in your relationship and that might be reflecting in his questioning attitude. On other hand he may be a suspicious kind of person. Let him know that he is hurting you by such attitude. Start talking about future of your relations i.e. whether you are going to marry? When? How? Etc. This will give clarity and reduce anxiety. If you are planning to break then tell him clearly mentioning reasons and stop all forms of contact. It may look difficult initially but if you are sure and clear from within then time will take care.