Straight man here in relationship of 40+years. I'm 65.
Had a couple of female colleagues in the last 20+ years with whom I've been sufficiently friendly that we mutually confided in one another over family etc and have seen outside work for coffee or drinks/meals in the pub after work.
First of them is a bit younger, forties, and was regarded as 'phwoar' attractive. Serially monogamous. We worked together in various roles from 1989 until 2010 bit remained, and still are, in touch.
No spark with me. We were just friends although there was a frisson not present with male mates.
My Mother, born in 1926, who was aware of my friendship worried about it. She was though brought up in an era where women couldn't go to the pub alone and being out/about with a man who was not your husband was social death.
Other also younger, fifties, very happily married. We were pally in the office but thrown together in the pandemic WFH but chatting in Google. We both appreciated each other's company and support in those odd times. With hindsight we got too emotionally close after the pandemic and I wonder if colleagues thought we were 'going over the side together' but were not.
Again no spark but that frisson was there again.
In both cases my partner knew exactly what was happening and ribbed me incessantly about the other woman!! She has male friends, albeit some of them gay, and the ribbing is two way.
One of my kids, referencing the second, introduced me to the term 'work wife'.
In short, if one's significant other is going to 'play away' then they'll do it.
Just having a close friendship with a colleague of the opposite sex ain't bound to go that way. In fact I'd say far less so than meeting OW socially.
Just accept the friendship for what it is and ensure your DP is being open.