One possibility I haven't seen mentioned...do you think ExH's current W/OW might already know about the affair? The solo trip certainly raised your eyebrows and you've suspected his cheating on her before. Perhaps she's noticed as well and is doing her own spying. It will come out eventually.
or perhaps they even have an open marriage ... no one ever really knows what goes on between a husband and wife.
M 20+ T25+ S ~15.5 (BD) BD 4/6/15 D 12/23/16
"Someone I loved once gave me A box full of darkness. It took me years to understand, That this too, was a gift." ~ Mary Oliver
