And this is why I am such an enthusiasts for RAW...I'm ruling that by spending an action searching, succeeding on the investigation check, and being adjacent to you the entire time, he can locate you well enough to get an un-disadvantaged attack. I'll grant that it's sort of awkward to make a ruling that ends with you being reduced to 0 HP, but I'm hoping your comrades will remedy that. And the forthcoming experience for the encounter should help too.
And this is why I am such an enthusiasts for RAW...