Wife has new male best friend

I am hoping someone out there can give me their unbiased opinion. This may or may not help me from going out of my mind.

To begin with, i have been married since 2009, my wife and I have always been on separate ends of the 'emotional spectrum. She tends to me highly emotional whereas i am on the complete opposite end. Despite the differences we have made it work well and kind of balance each other out. However, from time to time it does create some tension.

Over the past couple of years my wife has attended a personal training group, which is great, she has always suffered from social anxiety so to see her enjoy being around a new group of people and to witness the improvement of her mental health has been fantastic.

However it did not take long until she started spending time with a male friend from this group. As well as group sessions, they meet on non group days and train together alone for up to 3-4 hour sessions. This usually includes lunch, coffee, etc. So they end up seeing each other everyday whether in a group or not. This also includes texts and phone calls throughout the day.

I have questioned her about this. and have told her i am uncomfortable with the frequency, not necessarily the fact she has a male best friend.

She has told me that they do have feeling for each other, they have discussed this in detail and have vowed not to act on it. They recognise that it is natural that and two people spending this amount of time with each other are bound to develop feelings, however its whether they act on it or not that counts. This doesn't sit right with me. Just because you have recognised it, and have been open with me about it doesn't make it right or less hurtful.

This male friend has the emotional personality traits that i dont have, so it makes sense that she is attracted to him and wants to spend so much time with him.

But where does this leave me? I cant help feeling she would rather be with him than me? why wouldn't she, right?

Is she better off with him?

I dont want to stop the friendship, 1. due to the improvement in her mental health, 2. why should i? if my discomfort isnt enough, shouldnt she recognise the problem a pull back?

over the past 6 months this has put me in a depressed state, and if anything it has put more distance between my wife and I. I cant help feeling that without this guy out of the picture, we can not repair our marriage. I am seriously considering leaving her, but have two great kids to consider also.

Please help!!