Forget the one night stand sweetie... 15 years ago, before you were married? Come on get past it. To be honest I don't understand why he bothered to confess it now after all this time.
Porn.. well men do porn, can't see the point of it myself, (i'd rather be doing it than watching it
) but men are more visual than us females, and it's a pretty normal thing for most men.
I get the impression you are a little bit of an innocent, so when you say porn, are we talking really dirty nasty stuff, or just pictures of naked ladies?
I think that your hubby's sudden confessions are perhaps his way of dropping a hint or two that something is amiss, perhaps he is feeling a little unwanted or neglected, needs to talk to you about it and doesn't know how to bring the subject up.
You must swallow your inhibitions about this stuff and sit down to talk to him about it. Perhaps after 14 years where you have settled in all comfy, he feels like he is missing out on something. Sort it out with him, before he feels the need to look elsewhere.