Hi lido78.

Porn for guys isn't usually a replacement for sex, at least among guys I know (including myself). It's more like a way to blow off steam. You will find porn or links to it (assuming no housekeeping has been done to delete it) on pretty much every guy's computer, even happily partnered guys who have sex every day. For most guys I know, it fills a different need than actual sex. Sex is much more about intimacy and love and mutual satisfaction. Porn is about getting your rocks off. Don't worry about porn.

What you can be legitimately worried about, I think, is the decline in actual sex, independent from anything to do with porn. I think you'd want to ascertain whether it's really about his job or it's something about the relationship. I think the only way you can address that is by talking with him about it, and if he won't talk, well, that's a problem. No need to talk about the porn, though.