Re: What to do?
You should get a copy of those chats/emails. You can just take a photo with your cell phone if nothing else.
Next, if she backs up her iPhone to a desktop or laptop using iTunes you should be able to get a good look at what she's been doing. I am not an expert on accessing it, but it will be on her computer. Do a web search for where are iphone backup files stored on mac (or windows if applicable). There are ways to extract the data. You may need to purchase a program to do this.
Two significant issues here that I see. 1) Your wife is willing to go meet men for nefarious reasons. This requires you to quickly determine how bad it is, and to interrupt it. 2) Your marriage has problems which need to be addressed. Note that if she is doing what it appears she is doing, problems in the marriage are not the cause. Whatever imperfections you have as a husband are not causing her to go meet men in bars. It is not your fault. So, there are two issues to be worked on if the marriage is to survive. One is why she is capable of crossing these lines, and how to heal the relationship with you for having done these things. The second is for both of you to learn to be better spouses so that the future relationship can be much better. Don't let anyone (especially you!) try to lay the blame for her actions on you.
You could put a Voice Activated Recorder in her car, very well hidden so she doesn't find it. You could put a VAR in the house if there is a place she makes voice calls. You could put a GPS tracker on her car, though it seems you know where she is going. Those measures would give you answers within a week about what is going on.
There is merit to confronting her now. But, she will deny everything and she will become much more careful in hiding anything. The #1 rule is to never divulge your source of information. So you'll have to find a way to not say you looked at her phone.
One approach would be to say you want to spend more time with her, and while you are happy she has friends you are seeing your marriage being cut out of the loop. Her friends should be an addition to her social life, not a replacement for the marriage. Thus you would like to go out with her, perhaps with some of her friends even (or just the 2 of you).
Her friend who is enabling her with this other guy needs to go. She's toxic to your marriage.