There is never, ever a good reason for a married man to take anyone but his wife out to eat. Why do liberals think it’s sexist for him to honor his wife? My wife and I practice the same rule. I’m sure there are many lonely divorced men and women who wish they or their ex had followed that policy.
I think every successful loving long term couple has some spoken and unspoken ground rules that work for them. They may vary somewhat from couple to couple, but what works... works. End of story.
It’s not unusual at all for business people to go out for a meal together. The key is to always include a third person (or more).
It is always good for a relationship if both partners maintain both fidelity in fact and also fidelity in appearance.