That last line about it being 'weird' - it's not weird. It's him admitting without realizing it that he's lying, and that he knows you know he's lying.
Regarding 'forgetting' - I don't buy that for a second. If he 'forgot' he was asking to join couples in sex on that site, he was on a lot more sites and doing a lot more than you've discovered yet. I think he was hoping the evidence wouldn't be able to be discovered, so he lied. When his lie blew up in his face he used the pathetic and overused 'I forgot' lie.'
I'm so sorry for all of the pain you must be in based on your discoveries. His behaviors and his continued CYA actions make me feel like he's still in a very selfish mindset. I really think you should start the 180. It's very easy for a BS to let their entire life become about the discovery of more info, the search for the truth, etc. I realize that it's nearly impossible this early on to not be overtaken by the enormity of an A (or several As). I wish I had done a bit more detaching early on. I think it would have done me a world of good to keep some part of me (without the A nightmare) alive and active. It would have helped with setting and maintaining boundaries, and it definitely would have made me stronger, since the A took every bit of strength I had and destroyed it.
A side benefit of the 180 might be that your WH sees you pulling away, realizes his lies and hiding the truth from you are actually causing him to lose you instead of keep you. He may see that you're pulling away and begin to work toward healing instead of working toward keeping you in the dark. The 180 is NOT designed as a 'wake up' tool for 'foggy' WSs, but it has definitely had that effect.
WSs that remain selfish and 'foggy' honestly believe that their lies are helping them. They think if they can just keep the story up long enough, we'll tire and move on. Nope - the opposite is true. We BSs will dig for months or years even to get the truth if our gut is screaming that we don't have it. If your WS realizes you aren't about to stop, and that his lies are pushing you away, he may decide the truth is the best option. The 180 will definitely make him feel like he's losing you - because he is! You're detaching. If you detach and are able to objectively see his bullshit for what it is, he will suddenly feel foolish telling such obvious lies to someone that is seeing everything for exactly what it is.
One theme that remains constant is that a WS that is selfish and holding tightly to their lies after DDay will almost always stay right there, lying and being deceptive, for as long as possible. How long is 'as long as possible'? Until there are real consequences. If your WH lies, and you know he's lying, and his only consequence is you getting upset, crying, making threats that don't materialize and then giving up out of frustration, then usually the WS is willing to ride that storm out. If, however, the WS feels the BS pulling away, or even leaving, then there are real consequences.
This site is riddled with tales of BSs that tried and tried, with no results. The WS remained 'on the fence', not transparent, lying to protect themselvess, and basically refused to actually help the situation. When the BS finally stood up and refused to accept this terrible behavior, and told the WS to leave, or left themselves, started the 180 (and the process of detaching), or some other 'real' consequence where the WS knew they were on the edge of losing the BS, the WS woke up. Is that a guarantee? Nope. Should it even be the goal of the 180? Nope. But, imo, consequences are a MUST of a non-remorseful WS is going to 'get it'.
The 180 seems scary. The thoughts of 'what if he doesn't care, or nothing changes, or just leaves, or goes back to OW if I ignore him' are scary thoughts. What's scarier is spending a year, two years, a lifetime with an unremorseful WS. Imagine spending another year in this hell of your mind screaming that you're being lied to and your WH caring more about keeping his lies than about your healing. Not a fun thought, is it?
So, if you begin the 180 and start detaching, you're deciding you wont spend your life in the nightmare your WH is maintaining. If he doesn't wake up and change, you're already moving forward and detaching from him. If he does wake up, he's learned that you do have a breaking point and that you won't just 'accept' whatever he's offering.
If you haven't read the 180, it's in the healing library under 'FAQS for the BS' - I believe it's item #11.
You deserve better katiescarlett. At a minimum, you deserve the truth.