Re: Where there's smoke, there's fire
"And increase it to six times a week" -- indeed
A "change" - up or down - in your sex life is a red flag. If 5 a week is the norm, then that's cool. If he's suddenly more interested at home, it could mean that he's getting worked up elsewhere but still choosing to come home to you - for now. That was my experience. Wife flirting or "something" online - got her all excited at home. Was a lot of fun until you realize why you're getting so "lucky."
The office behavior - not sure. I don't like my wife coming around where I work. We just don't really have visitors. Its rare and seems awkard. And "I don't know" could just mean that he doesn't know how to explain this to you without hurting your feelings.
Now - her not looking up - I think you're dead on correct.