Most people accept the fact that marriage means your spouse and children become you number one priority. It's always been that way.
Not many wives want their husband running around with female friends or even male friends all that much. The same holds true for husbands. Very few men would want their wife hanging out with another man or constantly running around town with her girlfriends.
Having said that it all comes down to personal choices. In order for a friendship to exist (both) people must make the effort to stay in contact. Nevertheless this is very difficult for (friends of the opposite sex). As I mentioned earlier when someone loves their spouse they want her/him to be happy. If associating with someone is going to cause friction in their marriage they will generally choose holding onto their spouse and family over holding onto their platonic friendship.
Some people choose to have a "secret friendship" which usually entails hidden romantic feelings or sexual attraction. They are aware that their spouses would not approve of the "friendship" and therefore they engage in "emotional cheating" which can eventually lead to physical cheating. Rather than having to deceive their spouse many people opt to let those friendships slide. The other alternative is to incorporate the friendship as (couples). If it's truly a "platonic friendship" this should be easy to do unless the ex is a former lover or love interest. Not many spouses would like that.
Ideally everyone should have more than (one) friend or family member they confide in. Losing a friend or dramatically spending less time together should not be the end of the world. Hopefully one's spouse is their (best friend).
"If you have to get out of bed to talk to your best friend then you have married the wrong person." - Unknown