I am 21 years old and have had one LTR. I've dated dozens of women for short periods of time and taken hundreds on dates, and you know, I think I'm doing just fine. Don't worry about LTR's and Sex and Dates; just go have fun with women and let people call it what they will.
A name is just a name. If you end up dating someone for the rest of your HS career so be it, and if you end up never having a GF and spending quality time with dozens of women, so be it. Just remember, when it stops being fun, it's time to take a good look at moving on vs. trying to salvage something.
If I'd taken a girl on two or three dates and realized she was just dull, I'd probably LJBF her, but if we'd been dating for a couple of weeks, well, i might put some more effort into it depending on what else I had sitting on the back burner.
The point is, once again, you're young, have fun, enjoy the female species, and try to live so that twenty years down the road you can say, "Well, maybe I never went the whole nine yards with her, but damnit I tried, and that's all a man can really do."