someone please explain ( maybe a guy's point of view )

im seeing this guy seeing being the word here, we ment through a friend both do casual modeling and have pritty busy lives, we do heaps together see each other a few times a week niether of us are interested in other people have heaps in common love being around each other,
BUT i dont get it, if your seeing someone and niether of you are seeing other people, then arent u a couple and shouldnt u be classified as boyfriend and girlfriend? how long sould you be " seeing" each other before u are bf and gf is there a time frame? someone please explain.