So, bit of a long story.
I had a female friend who lived across the road, sadly her husband died from cancer and we were quite close - frequent wine night at her house, walking the dogs, shopping etc. She needed odd bits doing with her house and I asked my husband to help. Fast forward a year, she moved a little further away (5 miles), and we continued our friendship (wine night and occasional nights out) and my husband would go round and help her when she asked me. A few months later, my husband got a job at the same place as her and they frequently called each other work-wife or work-husband which never bothered me.
About a year ago, my husband started complaining about her (word related) and complaining about our nights out and how she shouldn't act that way at her age (I'm 33, husband is 41 and friend is 50). I eventually stopped going round for wine nights and he has continued complaining about her doing this or that at work and making it sound like they don't talk unless they have to.
Now on to yesterday - I saw my husband's phone messages from her (yes I looked which I feel awful for, but now I think there is a reason I made the decision to look). They have been exchanging messages calling each other work husband and wife, with lots of x's, and in one message he said something along the lines of "order me round to do it, I'm your work husband and have to perform my marital duties". I didn't have time to see more as husband realised he didn't have his phone and came back upstairs for it.
The last few weeks, he has also been muttering about women being cheaters and they all do it. Keeps referencing a work boyfriend I have, which I don't - I work remotely too. Am I going crazy and being paranoid, or is this normal behaviour?
For context, we have been together and married for 11 years and have two children together.