I'm not a veteran here, but since nobody else has answered, I'll give it a try:
It sounds great that you have taken well care of yourself. The saying around here is 'become a partner that only a fool would leave' - meaning, show yourself from your best side.
Have a positive attitude, have plans (personally, I wouldn't date or pretend to date - I'd go out with girlfriends and do things with the kids, but I told my H that I wasn't looking to date, I was committed to my marriage as long as I was married).
Be informed. Know your rights, know what you need in order to become independent, use your support system. The more you know about your future, the more you feel that you can manage, the more confidence you will exude. But let H take the lead - you're not interested in getting a D, so don't make it easy for him.
When it comes to communication, I would be straightforward but keep it positive. The way I behaved towards H when I found out about his affair (he tried to say we were separated while I was away for a few months), was to answer his questions clearly, ask questions, but not throw fits or get upset. The calm communication helped demystify the A and OW quite a bit, I think.
My overall attitude was: I'm committed to saving my M. It will require work and I think I will be able to forgive, but H will have to do his part and things will have to be very different - obviously we were both unhappy and we have to figure that out.
And I have to wonder... He went to visit OW - is this the first time he has seen her? And he's coming back for a few weeks on his own initiative? I wonder if it wasn't so great there after all... But don't let him think you suspect that, if you do.
Does your D live nearby? Is your son also his son?
M 16 yrs, WH62, P54 3 adult blended kids EA 11/13, BD1 6/14 PA fall 14, BD2 2/15 Piecing 2015, BD3 12/15 Separated 4/16 WH moved OW in 5/16 Divorced 6/15/17