It's not an expectation that someone pay. It's a cultural signaling device in other cultures that I think are not as forward as you are?
If you're an American or French or German or Irish, or any number of other nationalities, you might find yourself on a date with someone, but we don't talk about that kind of thing, sometimes for months. Particularly in the Southern U.S., people don't discuss that---they might just spend time with someone, but it's not clear what's going on there. If the man offers to pay, then it's clear it's a date.
You don't seem to be aware that cultural standards for that kind of thing are generally a lot more conservative than they are in Scandinavia. We don't for lack of a better phrase, sleep around like you do.