You see, you're making some assumptions about his weekend (he was having a fabulous romantic time with OW). And while that MIGHT be true, if you BEHAVE as if that's what you believe, you might screw things up if what REALLY happened was one of these scenarios instead:
1) Maybe he had a crummy time with OW who was clingy and pushed him into staying when he really missed his kids
2) Maybe there was some honestly legitimate work excuse and he's been working hard
3) Maybe he just spent the weekend breaking up with OW and is coming home to tell you he wants to reconcile (maybe not the most likely, but it could happen!)
If you KNEW that 1, 2, or 3 was true, you would be happy and perky when he came home, right? But what if 1,2, or 3 was true and he came home to you being grumpy from assuming he just had a romantic time? It would likely mess things up, right?
On the other hand, if that's really what happened, but he comes home to happy perky you, it still might make him rethink things. So - always a better choice to Act As If things are okay, in this kind of situation.
(P.S. I would "stage" the house - music on, glass of wine, dancing around the kitchen making dinner - whatever it takes to make it look like the cozy warm happy place he should be missing)
