B...I think the advice you have been given here is EXCELLENT! I agree with it all. My H, two years into the covert depressive phase is yet to admit the OW is anything but a friend, but I know better. Honestly, while knowing is hard and devastating at first, now you know what you are dealing with. Believe me the "is he or isn't he?" place is no fun and has threatened my sanity several times.
I, too, have gotten the business-like e-mails like your partner sent. He always has a reason to contact, but the longer this goes on every time he sends a business text or e-mail it is an excuse to contact me as he will then ask me some more casual personal questions. As the acute phase of separation wears off you may find this to be true (depending on what contact type he falls into). Since he's not hiding the affair anymore he'll probably run and party for a while. HAVE NO EXPECTATIONS. That is hard, but as the good book says, "Sin is fun for a season", but only a season. Like others have said, this is most likely temporary. It does not mean that they will not try to legitimize their relationship, but they will hit a wall sooner or later, especially with a MLCer in covert depression. The excitement will wear off...everyday mundaneness will set in, and the party will be over. Just be prepared, because that could take a while, and you have to decide if you want to wait it out.
I am waiting it out, but in the meantime living my life as if he's not coming back. Just this week I've decided to go a darker shade of dark (I work in the same workplace as my H so I see him during the workweek), and I'm already seeing him floundering because I've stopped being as predictable in my workday routine.
I agree with reading and re-reading the articles. They have literally been my life raft on days when I felt like I was going to drown.
Hang in there...you're not alone.