it has nothing to do with the fact that he is "foreigner". I know tons of happily married couples of different nationalities. And it has nothing to do with the fact that he is muslim, especially since you say you are a muslim too. What's the problem?

I am married a muslim (and I am not a muslim), and he is a "foreigner" too. His mom loves me more than even he does :):) His brother is my good friend, as well as his sister. 
You mentioned, you guys have no kids.. is that his decision not to have kids? And how are you going to continue such marriage? 
My opinion: either he is already married in his country; or even if he isn't, he has no any intention to tell about you to his family and friends, keeping in mind, that this "temporary marriage" will end one day, when he decided to have a "proper" family with kids.. Now its your choice either to accept it ( by the way, nothing wrong with accepting it, it is YOUR choice at the end of the day), or to step away. If you accepted this situation then at least you will know where exactly you are standing, and won't be suffering that much.