I genuinely think you're mistaken, in that case.
I don't think it's anything to do with same-sex relationships to start with, and I think language always follows trends - otherwise you'd have prefaced your post with 'Forsooth!' or something.
What does it matter? People use a word they feel is appropriate. Boy- and Girl- friend can seem a bit odd when you're knocking on a bit, and when you're committed long term, but not married, you maybe want to acknowledge the commitment with a word that suits. Also, it's a handy single word for both sexes. And covers married and unmarried people - fair simpler to say 'partners welcome' on an invite, than "boy or girlfriends, husbands or wives welcome".
There's also a nice statement in the meaning of partner - equality, cooperation etc.
Hardly worth getting worked up about.
On the actor/actress front, some women prefer not to have their profession mark them out as one sex or the other - doctors are doctors, male or female, as are nurses, barristers etc. There's no need to differentiate. Some women don't mind, some do - it's just polite to take that into account.