I was in a similar situation & my gut feel was right on. Learn from my mistakes!
Keep your cool & your anger in check. DON'T tip your hand too soon. DON'T let
on you suspect anything until you have EVIDENCE in hand. Take the opportunity
to make copies of suspicious emails, texts, phone calls. Find out who this person
(co-worker is very common), see if you can get any info using reverse phone number
search, is she married? Use the restore feature on computer to look over deleted
messages. Study him & get a handle on whether he's being evasive or acting weird.
Get the evidence to make your case & be sure about what is going on BEFORE you
ask him. If it's all okay then you won't accuse him unnecessarily, but if it's not then you
really cannot believe a word he says - liars lie - and you need proof for your own sanity.
When you are ready to confront, then do it from a place of strength - do not cry, do not
plead, be calm & collected & don't talk too much - HE IS THE ONE THAT HAS EXPLAINING
TO DO. DON'T try to fill in the silence, let him squirm but make him explain fully. He'll probably
try to blame you for his actions as a desperate resort to weasel out of responsibility - don't fall
for it. We are all responsible for our OWN choices & the predictable results. Things don't
"just happen" - we take deliberate steps to make them happen. We can't MAKE someone
love us, and we can't control anyone but ourselves - try to detach from the situation, it will
make a huge difference if you can accomplish this.
If this woman is married then make it clear that her husband deserves to know
what she is up to. Tell your husband and this woman in a very calm manner (in writing,
it's too hard to keep your cool otherwise) that this is what is going to happen - cold, hard
evidence (email copies, the works). This could be the cold water needed to nip things
in the bud hopefully.
This is all easier said than done - believe me, I didn't follow this to a "t" myself! I hope you
do better & come through it stronger & with all your dignity intact. If suspicions turn out right,
then you will have some decisions to make about what you're willing to live with and whether
it's worth the price. Only you can make that decision - think long & hard and seek objective
counsel (friends are well-meaning but might not be best advisors).