I've been re-reading your original post, OP and I also want to say, please don't assume that because your H is never late home and is always at work, that he hasn't been seeing this woman. He could have taken days off work without telling you (and her the same) and he could have left work early, so that he could meet her and yet still be home on time. I have known this to happen a lot.
Like others, I'm intrigued about this "rough patch" and also a timeline for all these events. You see, you've only got his word for it that this has been going on for a month. I've also lost count now of the amount of people I've come across after a discovered infidelity, who cite problems in the relationship before their spouse was unfaithful - and take the blame for causing those problems, especially if s/he has gone off sex.
At the very least, this has meant that the faithful partner ise discounting the friendship/mirroring stage that precedes every affair and also the pre-affair permission-giving stage. So the betrayed spouse sets the clock too late, to coincide with when the affair allegedly started. It then emerges that the reason the relationship hit the buffers was because of the distancing behaviour of the soon-to-be unfaithful party.
In plenty of other cases, it emerges that actually, the affair was going on for much longer than was admitted; years in some cases.
The end result is that a deceived spouse erroneously believes that their own behaviour was causative in an affair occurring, when it turns out that this was merely a response behaviour to their spouse, who had been trying to create a gap in the relationship to let the affair partner in.
In your case then, I wonder was this affair well underway 3 months ago - and that the friendship/mirroring stage and pre-affair build-up started long before that?
Try and establish the date he first saw and spoke to this woman and get your diary out and try to remember what your relationship was like before he even set eyes on her.
And tell us within this entire timeframe, when you first discovered the porn and the dating site registration.
I agree that it is worth pursuing why you went off sex and lost your mojo. Like others, I wonder whether this was a response behaviour to something that was happening with your H. I'd also be interested in your recollection of when your H asked for sex and you refused. If lots of these occasions were at times when he knew pretty well you would say "no", such as waking you up when he came to bed or wanting sex when a child could walk in at any moment, this is a lesser-known manipulative trick to set you up to fail.
Other "tricks" in this regard are if he ever used to ask for sex after a day devoid of non-sexual affection, general intemperate behaviour on his part and wanting to have sex with you seemed aberrant. If and when you said "no" which would be the most reasonable response in the world after a day like that, he might have sighed and huffed, but in reality he knew you would say no, but wanted you to take the blame for it.