Well in my case at no time and in no way was there an issue. All involved had solid & appropriate boundaries and mutual respect.
As a man you must evaluate your comfort level and what you find appropriate. My husband was friends with other/prior women as well. Neither of us cared or were bothered by this at all.
My larger point (which seems to have gotten overlooked), is that when you are in a healthy exclusive relationship neither the man nor the woman is going to have much volume of communication with friends of the opposite sex anyway. We saw my old lover a sum total of 5 times or so over 16 years...and the only lengthy conversation I had with him over the phone was to discuss career options in my field for his wife, so not a conversation about anything other than his spouse.
What's going on with OP is different. She is lying and justifying. That's the problem.
One of my sisters met her husband because she dated his brother (that is how they met.) After things fizzled with the brother her now husband asked her out. That brother is now her BIL and my sister is close friends with his wife. They are next door neighbors and trust me all is above board & has been for 25 years.
You have to look at individuals. I don't think the gf in OPs post is respectful...I just know there CAN exist respectful & appropriate situations...that is where individuals behavior is more relevant than trends or generalizations.
That's my bigger point.