Got woken up by our dog barking Solost and couldn't resist seeing if you'd got back, so here's what I typed out just before bed, to send to you in the morning:
Solost can I start by saying that I admire you for acknowledging that although what I write isn't what you want, you feel it is what you need. I'm also glad you're going to think about all this a bit more.
I'm afraid I'm going to dismantle his story even more. On your earlier thread, when I provided an alternative version of the affair where he directed events and let the OW take responsibility, you yourself agreed that between meeting her for the first time in the November and that first trip in February, there was contact. This is in fact what you said on that thread:
"There probably were emails between november (when they first met) and march, I knew they had a few work related meetings too, but others were always present. H did say once she used to ring him and if he was driving she could be on the phone for up to 2 hours 'just talking about her life, how lonely she was, how badly other men had treated her'.
It is therefore a complete lie that there was no contact between them from November till February. He has previously admitted to you that there were work meetings. Perhaps he forgot that little slip from months ago?
Consequently, it is fantasy that the first time he knew she was on that trip was at the airport. Just as it is fantasy that the first time he became aware of her as a potential affair partner was on that trip.
I wonder whether you have missed something in something else he said, about the second trip and taking her back to her room?
He knew something would happen, but thought he would go 'so far' and pull back??
Well according to him, he did pull back. He says he kissed her and slept on the chair. Not that I think he did just that, of course.
I'm sorry Solost but I think they had sex on that trip and I think he is lying through his teeth about there being no penetrative sex until after he left. I have heard of men starting their affairs in this way, to allow the pretence to linger a little longer, that like Bill Clinton, they haven't been technically unfaithful, but I have never known of that lasting, especially in someone who goes on to leave for the OW.
Why would he lie? Precisely as AF says. He wants you to believe that right till the end, he still had "some scruples". It's not important that he believes this, because of course it's a lie, so he can't. It is however important to him that you believe it and can still be manipulated by his lies.
As for the phone calls, that's a lie too. He knew full well what those calls were about and made them too, plenty of them. I am convinced that by that time, their relationship was highly sexual and would not have been mundane interactions at all. Even his colleague, hearing a vastly sanitised call on the speaker phone, knew it was dangerous and told your H so.
The laptop E mails don't surprise me though. E mails are still not regarded as being as "safe" as text messages and if they were originally forwarded to his work inbox, it wouldn't surprise me that they had a pact to send anodyne communications between the companies rather than risk some systems manager doing a search of people's inboxes. Some organisations even have quarantine systems in place for messages that contain non-business terms, such as "love" or "sex".
You said a couple of months ago that by May, he was already thinking of leaving you and was telling OW that he would. Even in the grip of an enormous crush, I find it hard to believe that he would have left within days or weeks of the relationship becoming physical. He might though, if he had been involved in a full emotional and physical affair for 3 months.
Paltry though that 3 month timescale was, it must surely be more palatable for you to believe that it at least took months rather than days or weeks for him to decide to leave you? This is a prime example of when I say that the lies that people tell actually show them in a worse light than the truth. If he thought about it, how bloody awful does that make him sound? That he would decide to throw away 27 years and 3 DCs for an affair that was less than a month old? 
Yet this is what he wants you to believe.
What would I do? This is difficult because I have come to detest your H over the months and cannot imagine I'd feel any differently if I met him in RL.
Dog settled down again now, so back to bed. Thank God it's Saturday tomorrow 
However I acknowledge that you don't, more's the pity. Therefore, I can only try to get inside your head and imagine what I would do if I still thought that this man was worth having.
It sticks in my throat, but this is what I would do if I wanted him back.
I would start divorce proceedings. Apart from the expense, I wouldn't care a jot if it progressed to divorce. The old marriage would be dead anyway and I'd have no desire to hang on to it. Any future relationship with him would have to be new and different, but at least if that didn?t happen, I'd gain an equitable financial and childcare deal.
I would change the locks and tell him why.
I would ask the DCs how they wanted to see their Dad and accord with their wishes. If they wanted to see him at home, I would get an internal lock on my bedroom door and hide all my personal stuff in there.
I would go out every time he came round.
I would get some urgent solo therapy.
If he dropped any more hints about regrets, I would tell him that he can never come back. Hence, if his relationship is on the rocks, that must come to its own natural ending, but it would have to be him ending it and not her.
I would wait to see if it does end and watch him move to a flat nearer his children, insisting that from that point onwards, he sees them there and not at your home.
I would watch with interest to see whether he got any solo therapy.
I would spend months trying to create my own life, seeing friends and meeting new people.
If I still loved him after all that and he had dismantled every personal and lifestyle vulnerability to future infidelity, I would start dating him again and draw up some groundrules for a completely new relationship.
I would tell him to stop lying about what happened during the affair and once and for all, to tell the full truth. If he then rehashed the crock he gave you on that O2 trip, I would walk away and not look back.