I hope this thread is either a joke or a bad attempt at trolling.
boyfriend/girlfriend is a disgusting terminology for any Jew, especially one who purportedly is Torah observant.
How can anyone who isn’t a Chasan/Kallah (and aren’t married) even dream of calling themselves that?!
There is no other terminology because it is highly improper to call them a thing or to allude that they have any improper relationship, which giving them a joint term would clearly imply.
You shouldn’t even be making public that you are dating her, as that’s no third-party’s business and it wouldn’t be tznius to let any one know.
That’s all before the question whether you’re even “dating” too long before you need to make a decision one way or another.