wife in workplace EA

Hi all, a brief summary of my situation. I would just like some simple pointers as to what my ultimate move should be (am prepared to play the long game if necessary). Some of this info has been accessed from cell phone texts (not exactly ethical I know but my therapist was OK about this, saying it is the lesser of two evils):
(a) OM confides in my wife about his "unhappy" marriage, tells her he fancies her, she is shocked and then flattered
(b) she engineers it so that I drop her off at her work Christmas party, the obvious then happens
(c) obsessive phone behaviour over Christmas and New Year so I look at Whatsapp, long amorous conversation found
(d) I confront, she downplays, said she's helping him sort his marriage (she does not know I saw Whatsapp conversation, in fact to this day she has no idea what I know), she would never leave me (hmm), apparently workplace relationships never work, she says she has not been to his house
(e) second confrontation a week later, apparently OM is told that I have to be the priority, she justifies hookup by saying "I was depressed at the time" (true, but no excuse of course)
(f) affair has snowballed (limited opportunities, e.g. lunchtime walks, fumbling plus worse in disused work rooms)
(g ) is now physical by definition but apparently not full sex (yet)
(h) would appear OM has no plans (yet) to leave his wife
(i) do I confront again now (presenting of text evidence may seriously backfire with her, also some family court judges may take a dim view of this and deem it illegal) or wait for implosion/affair discovery by others (I can forgive in principle, we have a 7 year old daughter to consider)

thank you in advance