Hard to say (no pun intended) - it could be his Testosterone level has dropped to a point he's just not very interested in sex. However, 45 seems relatively young for that to happen, but it does sometimes happen to guys that age or younger. If he's especially stressed at work, that can definitely affect Testosterone levels & libido, so that may be a factor in this as well. You raise the possibility of porn-related ED - it is true that some guys get kind of addicted to porn & over time, nothing stimulates them enough to get interested or able to achieve suitable erections. It's a shame that he won't talk about this - that's a mistake on his part. But also, it sounds like you're kind of pressuring him for sex, and that is not helpful either. I know guys are sensitive about so-called 'performance' issues (that's a bad word, 'performance' - it implies guys have to 'get it up' on command, which just doesn't always happen, especially as guys get older), so that may be why he refuses to discuss it - he probably feels ashamed & inadequate, which is devastating for men.
You need to let him know you really love him & care about him & would like to find a solution to this issue without getting angry or pressuring him. You should lovingly tell him not to be embarrassed about this - it's a pretty common problem based on the number of ads for Viagra, Cialis & numerous over-the-counter 'performance enhancing' supplements. Back to the porn thing for a second - do you know for a fact that he's looking at porn? I know wives & GFs hate the idea of it, but unfortunately, the majority of guys do, at least to some degree.
I think the only way you two can solve this is to have frank, open, non-accusing, non-pressure conversations about this issue. Then if he's open to it, possibly see his regular Dr. first for an evaluation (possibly a Total-T and/or Free-T test) & then possibly a Urologist who specializes in ED-type issues. You may want to consider some type of counseling also, since this seems to affecting the health of your marriage. I wish you two the best - hope you find a solution. I'm sure NEITHER of you are happy about this situation...