Check out Pat Love's web site. In the downloads section there is a document about what defines an "office spouse". You and W may want to agree exactly about what is over the line and what is not. W may feel that texting off-hours with a male coworker is totally fine and to you it may be way over the line. If you don't discuss and agree in advance, you're headed for trouble.
It's important to make that discussion mutual. It's not about what she must and must not do. It's about what you *both* agree to do. You are both human, you both like attention from the opposite sex, you will both be tempted. It's what you do with that temptation that matters -- the temptation in itself is not a sin, it's being human.
The Pat Love document gives you a very good checklist for a very specific discussion about what is OK and what is not between the two of you.
After my W's EA, we reviewed the list and agreed on what's ok and what is not, and then agreed that if either of us are tempted by a coworker (or anyone else), that we will disclose it to the other person. When that happens, we won't be scolded or reprimanded, we'll examine if we have issues in our marriage that are contributing to the situation that we need to address, and if not, work together on dealing with the issue. One thing Pat Love recommends is getting together with the third party so that they get to meet you too -- that has all kinds of benefits.
You are in a precarious position right now, don't underestimate how much you contributed to this situation and how much you need to do, regardless of what W has done. If you focus on W, W's problems, and what W needs to do to restore your trust, then you're really missing the boat. Look in the mirror first. If you know you're the kind of husband that only a fool would leave, then you really won't care about keeping tabs on W and OM, because you'll know you won't need to. If you're meeting all W's needs and making her feel loved, there will be no room for anyone else.
Along those lines, I suggest you read "The Five Love Languages" -- it should be required reading before you get married. You should both read it and discuss it together -- it's quick and effective. It's also available on Kindle which you can read on your iPhone, blackberry, or PC.
Accuray
Married 18, Together 20, Now Divorced M: 48, W: 50, D: 18, S: 16, D: 12 Bomb Dropped (EA, D): 7/13/11 Start Reconcile: 8/15/11 Bomb Dropped (EA, D): 5/1/2014 (Divorced) In a New Relationship: 3/2015