Have read the whole thread and what surprises me is how much talk there is about his feelings. Ok, that may have been you in the first throws of the incredible hurt and shock. I hope you're past that now and focusing more on yourself and not getting dragged around so much by his drama.
Agree with peterandre that he (now I'm doing it!) is attention-seeking and thrives on drama. He was a 'tower of strength' when you were ill - of course! He was the hero! Incredibly angry that his immediate reaction was to share what is happening to you both with the OW. Incredibly angry. Boundaries, girl: she is off-limits, totally, in entirety, if he wants you, his marriage, his home, his family. Pleae don't indulge him in this puerile escapade.
He says he 'can't explain why' he's done this 3 times. (btw I sincerely hope he isn't still reading this thread or that you are still feeding bits of the thread to him -won't the man do any work for himself? Does he get this spoonfed to him, as well as teaching him how to be an unselfish lover etc etc??). He's done it because he is a baby and is quite happy to be a baby. He's thrown a big wobbly here and, guess what, he's got a lot of attention, which is what he's after. You are doing all the work valentine, all the preparation, all the soul-searching, presenting it to him ready-packaged. He's done none, is dithering about counselling, fussy that he 'won't like' the counsellor [ffs!], wants to talk to his fancy piece about incredibly personal stuff going on in your marriage 
.
I wholeheartedly agree with sympatico that feelings are entirely unreliable and can swing dramatically hither and thither (hence his attachment to them!). He says he felt words to the effect of warm and fuzzy at work, then on the way home his feelings changed. He took all the silliness seriously! Dear lord, that's what they do when they're on the throne, given TOP priority, knelt down before - which his seem to be - and you're doing it too OP. He's probably in his element (whether he looks tired or not: prolonged excitement can make you tired) - and you're colluding in that OP. Feelings are very often a con. After the first flush (the one he is wedded to?) a marriage is about commitment, not feelings; rejecting what jeopardises the commitment you have made. Being a grown up, basically. 'Feeling in love' is not what it's about, but being in love.
As for fancying someone at work - dear God, who hasn't? Feeling (there's that word again) you might be 'in love' - ditto. It's all tosh tbh. When you realise you are getting the very first twinges of noticing someone, you avoid them. Going to the photocopier? Go the long way. You can't play with fire and not expect to get burned, to get away with it. He can't afford to indulge that stuff. It royally pisses me off that people say 'it just happened'. No it didn't, it happened and was stoked the million times you made an excuse to walk past their desk, the moment your interest was tweaked and you made that first decision. So much self-deception in these grubby little work affairs imo.
Sorry I sound angry - I am. He's behaving like a kid and imo when kids play up you tighten up the boundaries big time. Really big time. Not nice, not nasty, but firm. He has to feel the consequences of what he has done ie unpleasant, uncomfortable consequences. Not lavishing him with time, attention and 'talks'.
Lastly DO NOT GO AWAY AS YOU HAVE PLANNED. Are you kidding? You'll be giving him acres of time to spend with the silly woman. No wonder he was so quick to suggest where you could go!
I am so sorry you have been dragged around by his juvenile behaviour - so painful. Your marriage sounds strong but for this significant flaw (and his underlying selfishness). I hope you work it out and that you make it abundantly clear that this 'flaw' won't be tolerated, is not an option. Ever, under any circumstances. Get the process in motion, even if it takes 3-4 months, to change his workplace and make it a condition that you expect him to step up and address this problem properly - on his own, like a big boy! If he does it again, he's out, and loses everything (not nice). That'll make him think twice on his way to the photocopier.