@Jumpingthruhoops
Regarding this male 'friend' of yours...
Why on earth do you 'message him daily?'
I don't even message my adult DC (who live 15-20 miles away) daily. We message each other every 3 days maybe. And my extended family I speak to maybe twice a month. And my friends I am in contact with probably twice a month, maybe three times. (We acknowledge each others Facebook posts once a week maybe in between, but we don't speak more than two or three times a month.. And we meet once or twice in between.)
Sounds rather obsessive, and somewhat needy, to be messaging a 'friend' every single day. I do wonder which one of you starts the messaging off, although I am sure you will say 'it's 50-50.' 
Do you really believe your DH is just deliriously happy with you messaging a male 'friend' every day, and his wife will be proper chuffed too (if said 'friend' is married?) Seriously, you're deluded if you think your partners don't mind. If they actually don't mind you having close daily contact with someone of the opposite sex, they're probably up to something themselves!
And no, it's not that we have not 'got past this idea' that men and women can't be friends, most people have no issue with that! But in the situation the OP is on about, her DH and this woman at work are not just 'friends.' You're hilariously deluded if you think they are - or if ANY man and woman constantly messaging every day (and meeting up alone together) are 'just friends.'
What's more, I know plenty of people with friends of the opposite sex, (including me,) and we don't constantly message each other every day. 🙄 (OR go out - just the two of us, without anyone else every time we meet!)
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