It's interesting for me to go back to this old thread. I can report back now, that while what I was seeing during H's visits and in between the visits, might have been bits of OW withdrawal, he didn't complete it at that time. She continued to contact him and probably manipulate him with reminders of their special friendship and pitiful tales of her own marriage (throwing up here is permissible!). He was also too weak and too lonely at the time to face OW withdrawal. He was not living here, but was visiting 3 or 4 days a week.
I can also tell you all that while many will display lots of the signs mentioned here, the extent will vary greatly. I think it was in kikki's post and an HB post that grieving is mentioned. I drove myself a bit crazy when the real OW withdrawal was happening because he wasn't displaying these signs to the extent mentioned here. Rereading this post caused me to think about it. I suspect that how they go through OW withdrawal will be very similar to the way they have grieved over other deaths in the past. My H grieves quietly. It's a bit odd really. One would not really know he was grieving as he seems his usual self. He simply goes on in quietness. I've seen this when each of his parents died. No tears, no discussions, nothing but perhaps becoming angry a bit more quickly than usual. This is how his OW withdrawal looked.
The exception is the day he ended all contact and told her not to contact him again. That day, he was a bit manic and afraid. He needed lots of reassurance from me that day. I didn't know what was going on until a few days later, but I knew something was up. I even said something to him.
The other thing I learned was not to mention her or to question him about her during this time. I'm not perfect and did this a couple of times. He did not turn back to her and did not run. I felt terrible doing it as I knew it was hurtful to him, but I also needed to ask about it for myself. We can only give so much as we are dealing with A LOT! There was also one piece of contact remaining that I needed to have ended. He wasn't utilizing it, but I knew it was possible that she could contact him still. He blocked her cell number and emails previously on the day the friendship was ended. (the PA had ended months prior) He ended that last means of contact when I asked him about it several weeks later.
So my point is this: watch for the behavior that is different. It may not look like what is described here depending upon the MLCer and their methods of grieving. Also, as others have said, I think this process generally last 4-6 weeks from what I've read.