Loves - thanks for the update. We really are rooting for you. I hope that despite your Dad's illness, you manage to enjoy your week with the children and GPs. Are you going to mention any of this to them? I'd love to think that you were going to get some mothering yourself this week and some TLC, but will understand if you say nothing too.
The E mails you uncovered are interesting, but not terribly conclusive. I bet you were frustrated at not being able to see more. What it does tell us though is that they are communicating more frequently than most work friends do - and in a tone that suggests a line has been crossed. Any idea what he said in the preceding E mail that caused OW to respond with the "I've got my head around it now" comment?
WRT snappiness and irritation with the DCS, yes, this is absolutely typical behaviour. Our dinner table became a regular battleground during my H's affair and it was horrible. When he discussed this shamefacedly with his counsellor post-affair, she concluded that at a time when his life felt out of control, he had a need to enforce it when he could - and the DCs were the easy target. At some point, this stress starts to leak out into relationships outside the home too - my H started over-reacting to slights at work that he might have previously taken in his stride - and he started having uncharacteristic arguments with people.
I'm glad you're reviewed the Relate option, but I want you to have another think about something now. You are saying that you hate conflicts and that your H will turn perfectly legitimate concerns back on you into you being suspicious and untrusting - that he is verbally dextrous enough to "win" an argument with you. This worries me as a behaviour in its own right, regardless of any affair-related behaviour. One of the things you might like to look at if and when you do repair your relationship, is that this is very controlling behaviour on his part - and quite abusive.
I believe you when you say that in 15 years, you've never had this level of worry. I suspect at some level when this friendship first started with OW, you consciously wanted to be the liberal, mature sort of woman who was perfectly fine about friendships outside of the marriage. You may have thought that jealousy wasn't part of your make-up and that since you trusted your H completely, it was perfectly fine that he had this friendship. Older relatives might have raised an eyebrow at you "allowing" a friendship like this, but you may have laughed gently at their old-fashioned ways.
And yet....at some subconscious level, it didn't feel comfortable. You perhaps tried to suppress those feelings, but they nagged away at you.
When those subconscious feelings turned out to be right after his drunken admission, your instinct was still to be cool and mature, reasoning that it's understandable to feel attracted to others at some point in a long relationship. However, you weren't getting much in the way of information and transparency from your H - and at this point, you allowed your subconscious instincts to come to the fore. At this point, it became "permissible" for you to view the friendship with suspicion, but instead of treating your concerns as the most normal thing in the world, your H responded defensively - and traded on your liberal, pragmatic nature. At some level, he knew that if he kept doing this, because at heart you so wanted to be cool and laid back and in the past have felt completely removed from a jealous harridan, you would revert to what you wanted to be rather than how you are.
I suspect this is why you did a very mature thing in meeting her in December. Even he was shocked at this - and she was even more shocked. This action sat comfortably with your view of yourself as a modern, pragmatic woman and not a hysterical, suspicious mess.
However, what I want to say to you is that you were right to have those nagging instincts - our inner voice is the thing we cannot deny, even if it conflicts with what we want to be. When you've worked through this horrible time in your life, you will accept that the only safe friendships are with people who wish the marriage well and are friends of the marriage.
Let's imagine OW was similarly horrified that her feelings had crossed the line with your H. She's got to keep on working with him, but she really doesn't want to endanger his marriage. She has some options if she feels this way - she could ensure that contact out of work on their own ceases, or if she didn't want to lose the friendship she has come to value, she reasons that the best way of continuing it is to befriend you. When you met her and told her that you knew what had happened, her instinct would perhaps have been initial embarrassment, quickly followed by genuine reassurance that she means no harm. To follow up with trying to build a friendship with you, even taking you into her confidence about girlie things such as dating as a divorcee. She would have done everything to persuade you that she was a friend of your marriage.
It sounds as though, beyond a few necessary interactions when you popped into the office, she did none of that. This is telling in itself.
You've got to the point Loves where you've finally given yourself permission to be rightfully suspicious. This is good - and as I keep saying, trust that memory of yours. That rational, level head will serve you well. You know that you haven't changed, that your marriage was happy until this all started. Even now, in the face of terrible provocation, you can still love.
One of the processes that might help you is to pinpoint a time when you last felt you and your H were at one with eachother - and when you were truly happy. When there were no "inner voices" and he was like the old H, adoring, affectionate, desirous, great with the DCs and sex was joyful and loving. If that timeline shows that this was at any point in the last 2 years after he took that job, there is your answer. Your marriage became unhappy after she came along - not before. Trust yourself on this Loves - many people might try to convince you that this doesn't happen if a marriage is happy, but they are not in your relationship and people have their own agendas for this belief. I'd bet it's OW's belief - it would suit her agenda to think that if your H had been happy, an affair would not have been permissible.
WRT your immediate situation, your account of the weekend just gone is illuminating. He's still managed to avoid the conversation you need to have about his behaviour. The old him might have been really worried that you were so unhappy and would have been making every attempt to try and reassure, even if he was never very good at "feelings" conversations. But the new, deceitful him will do anything to avoid reassuring, discussing or asking for your help to resolve his turmoil. The last thing he wants to do is confront what's going on, so he evades it. He has lost empathy for you and how you are feeling - it doesn't move him at the moment like it once did.
If this goes on without discovery or an admission, the woman you are will finally reject what is happening to her. That process is starting now with your glance at the property pages. He is losing you anyway, regardless of an affair. If you're right and he is terrified of losing his marriage, this is a terrific weapon in your armoury. You calmly stating that you have been giving this much thought and feel you cannot go on like this, might be just the wake-up call he needs. The thought of you living hundreds of miles away with the DCs might be more sobering than you think.
Communicate what is in the open domain. Say that you love him and want to work with him on this marriage, but he doesn't appear to want to meet you half-way on this. That you will not live with cruel treatment, constant conflict and behaviour that is damaging to your DCs. That you have tried over and over again to help - and have asked him to get help, to no avail. He will not engage. That is unacceptable to you and although this makes you very sad - and is not what you want - you will leave this marriage yourself.