As a woman with a LD husband, I am so familiar what you are going through! For me I would be major pissed about your son possibly seeing the porn. But on the other hand I would be able to brush off some of this as related to your husband. You don't really know if he is watching it to possibly get himself in the mood for you (he is trying) or if he is getting off by himself and leaving you high and dry.
This is what you need to explore with him, the men that choose porn over an available women usually do it out of anger or bitterness.
