Hi, Angelica - I think I have a lot to learn from you, the bit I know about your situation.
Do you mean that it is strange that he's had affairs in the past in general, or that it is strange that he doesn't seem to be having one now, as part of the leaving thing?
I only found out about all the affairs in September, when he told me he planned to move out. Before that, I had on three occasions found evidence of online affairs (totally accidentally the first two times, and the third time I just happened to come across something that led me to look a bit further). Each time, there was an increasingly big blow up. The last time, which was almost two years ago, he admitted to one PA.
We have done a lot of counselling, but I was never able to let go and move on. Partly that was because I needed some AD help, and partly because I'm sure on some level I always knew he was lying. I asked him if there was someone else 'waiting in the wings' and he said no. I'm pretty sure that he isn't sleeping with anyone else right now, but I'm also pretty sure that he has been doing the online thing again.
I am doing/going to do some reading to help me handle the infidelity in a different way and hopefully I'll get a chance to address this with my H in the context of a continued M.