My marriage is falling apart

My marriage is four years old and blessed with a son. We stay apart because of our jobs and he comes home about once a month. 

He does not want me visiting him at his station in Abuja and all my pleas fell on deaf ears as he claims that his house over there is not comfortable. 

I try to make up for the lost time whenever he comes home by being very nice and romantic and very creative in bed, but he is always claiming to be tired or wants to go out, so we may end up having sex once or twice if he stays for a whole week. 

He always complains about not having money. Although we are Christians, I think that he is having an affair in Abuja. 

What should I do?