NOTE: This question in NOOOO way has anything to do with any sort of hyper-feminist movement affiliation lol. On the contrary, this has nothing to do with any sort of "equality" issue but is instead merely an issue of "showing affection," so please don't even go there.
So i've noticed that a LOT of guys on here refer to their gfs or wives as "THE" gf or "THE" wife rather than "MY" gf or "MY" wife. I've never heard any of my friends use "THE" instead of "MY," and I've certainly never referred to my gfs as "THE" gf. It just sounds so impersonal and devoid of any affection whatsoever. Same with reference to my parents: they are "MY" parents not "THE" parents.
People even say "MY" dog, usually, instead of "THE" dog, the former once again showing more personal attachment than the latter. Usage of "THE" seems to render the subject in question as little more than an accessory -- the toaster, the shower, the computer, the X5, etc. Oh wait ... I even say "MY" X5
"THE" just sounds so ... unaffectionate. That really is the perfect word to describe my opinion on the matter.
Is it a regional thing? Out here in California -- SF, LA, and SD -- I've just never heard it before!!