If i got Pokemon white and i want to stay on that line should i get Pokemon black or white 2?
To stay online in Pokemon, you need to subscribe to Pokemon Dream World Guide. The Dream World Guide feature allows you to control both Pokemon Black and White. Visit http://www.thonky.com/pokemon-black-white/dream-world/ for more information.
What line? I have Pokemon White. (But only because I wanted a Zekrom...) Get both if you want. Then you wouldn't need to trade with people.