“I can understand why she could have been upset from a few of them as when I showed my friend she said they could have been viewed as playful. But it wasn’t flirtatious, it was just silly banter.”
So you can understand that his wife is upset, so you must be able to understand why she doesn’t like you.
He’s your good friend, your friendship with him is causing trouble in his marriage, as are your ‘playful’ messages, yet you don’t care about the state of his marriage? You don’t feel that if he hasn’t stepped back a bit, that as his friend who care about him and his marriage, it might be a good idea to suggest this to him? In your shoes I would tell him I was backing off with the messaging outside of work, doesn’t mean you can’t be friends at work but it’s hardly the end of the world to just concentrate on your own husband in the evenings and at weekends, is it? as it’s causing him trouble at home.
Yes, it’s his marriage and he needs to deal with it, but don’t pretend that you haven’t now been dragged into it, her being upset is actually quite a lot to do with you, with your choices and your behaviour as well as her husband’s. You could claim to be nothing to do with their marriage, right up until his wife started complaining about you. No, it’s not all you and he needs to rethink his behaviour and the extent to which he turns to you in the evening and weekends, but you’re his close friend, she’s upset and doesn’t like you because of what she sees as your inappropriately close relationship with her husband, you disregard and excuse this by saying it’s his marriage, his problem, but you’re not helping, you’re not in the least bit concerned about how upset she is about you, all you seem to care about is your close friendship with him.
You distanced yourself from describing this as an emotional affair, but seem to have an obsession with this man and your friendship to the point of writing a post about it here, where you listen to opinions but then justify yourself and show you don’t think you’re being naive at all, you already know the answer to that.
Add frequent out of hours evening and weekend contact, personal gifts, not caring about how his wife feels, or having the least interest in meeting her or getting to know her, (l know all my close friends’ spouses and would hate to think I was causing them a moment’s grief), excusing it all with ‘not my problem if his wife doesn’t like it’ and not the slightest hint of worry that you might be helping him cause trouble in his most important relationship, which is or should be his marriage to her, smacks more and more of an OW’s attitude, even if you aren’t one yet.