https://marco.org/2008/06/03/jessica-just-a-few-minutes-ago-i-heard-some-men
Just a few minutes ago I heard some men at the park discussing their buddy’s “lady friend.” I’ve been hearing/reading this phrase for a while now and I think its dumb. Just man up and call her your girlfriend, dude.
How old were they?
There’s a significant vocabulary gap when describing girlfriends above a certain age, especially when the relationship is serious and long-term. We just don’t have an appropriate word for some relationships.
It’s a bit strange to refer to the 60-year-old woman you’ve been living with for 10 years, for instance, as your “girlfriend”. And most alternative words have additional unintended meaning, such as “partner” (same sex), “lover” (it’s mostly physical), or “soulmate” (eternal, destined for marriage).
“Lady friend” is one alternative, although it does sound a bit awkward. (The same problem applies to men, but “man friend” sounds pretty stupid.)