I'll bet he's "using" internet porn. If he's good with computers and you're not, he could easily hide most evidence of this. Since I'm better with computers than my H,I easily figured out how to "spy" on his internet activity back in my days of crazy desperation. I'm sure some of the computer savvy people on this board could tell you how to do the same. I don't necessarily recommend this. It's a bit like opening Pandora's box, but it can be kind of helpful if it makes you angry enough to take action.
"Tell me, what is it you plan to do with your one wild and precious life?" - Mary Oliver