advice please

[CW2017]

Hi all
by way of an update the latest set of texts has confirmed my worst fears (and I'm afraid Sandi was bang on here particularly as she has used the increased sex not so much as to relieve her own pressure but to "distract" me). The physical affair is now tantalisingly close. She has let lust override whatever remaining morals she had left. So all they need is the opportunity outside of work hours. Anyway I digress. What I would appreciate most in terms of advice now is concerned with tactics. Our mutual cell company has an online portal for their app which works much like Whatsapp. We both deleted the apps from our phones as we didn't need it but what she doesn't realise is that the texts never disappear online and I will make out it is autologon with presumably the same password has her normal phone account webpage (not that I care now if she falls for this or not). So I now have all the evidence I need (it has also been screeengrabbed into a Word file as backup). It would of course be nice to get Valentines Day out of the way first (I have spent quite a bit so as to appear to be a "normal" husband). So clearly I want it to come out into the open on her part (it remains to be seen whether the OM will have the guts to tell his wife). The complication will be the disruption/tidal wave at this end due to our 7 year old daughter who is loving her school and her friends (my wife might want to move her?) plus, would you believe, her mother also lives with us (that has always been a source of "marital harmony"). So would she panic knowing I know? Based on other threads I have read here I guess in essence the marriage is over? I think it's worth fighting for but it might have to come after they get it out of their system where the reality and ups and downs of a real relationship replaces the fantasy one. In any case I have to watch my health now as I have barely slept since New Year and I get a bit of chest pain from time to time. I have now arranged to see a therapist (I am in London so I assume the term is the same although technically he would be called a psychotherapist). So all suggestions would be most appreciated! with many thanks