Update:
I want to thank you all for warning me it was very likely my wife was having sex with another guy.
She finally came home at 9:30 am and was rather silly, walking away and not wanting to talk. She would just laugh if I asked did something go on I should know about. Then she said she needed to ...... but she quite deliberately (I am convinced) left her phone on the table.
I checked FB messenger and sure enough, his message is the first and it says:
'Thanks for a great night! Let's do it again soon!'
To which she adds a smiley face.
She is no doubt trying to decide if she tells me that just means they had fun singing kareoke or admit it was sex.
Am pleased I came on here and you all helped me prepare more for this.