The rules are fairly clear on this even if they do allow for some DM discretion
Under Hiding
If the halfling pops out he can be seen clearly. You don't remain hidden just because at one point on your turn you were hidden. However there is an exception a few lines later.
This seems pretty clear to me. What those circumstances are will vary from DM to DM of course but I would never assume that the halfling can hide behind the fighter round after round. I know it wouldn't work if I were DMing.
Well I mean, it's regularly admitted by WotC that the Rogue was designed with the intent that they would get Sneak Attack every round by hiding, so... kinda screwing them over with that. At least for ranged. Melee works anyway because of an adjacent creature.