Considering all of this, idols (who aren't limited to just Johnny's) are much more marketable as single individuals, and it is quite easy to conclude that any talk of the relationships any of the boys might be having is taboo.
Especially in the case of Johnny's boys, whose fanbase consists of mostly girls and women, the availability of the young male stars is paramount. Otherwise, his fanbase may never pick up or is subject to decline.
That's why information regarding celebrities' personal lives is often limited to family and friends, and when the inevitable subject of a girlfriend comes up for Johnny's boys, the answer is most likely something playful and indirect--they are never specifically dating one person or another. They may admire another female idol, or say that they are interested in a certain type of girl. This has become an extremely marketable strategy over the years, and is often included in many of the boys' profiles.
This 'hush-hush' about romantic involvement can be observed in China and Korea also, to an extent.
So, the answer to your question is...
No one is allowed to know if Yamashita Tomohisa has a girlfriend or doesn't have a girlfriend.
His romantic affairs in particular are going to be the hardest to discern because of his extremely popular stature for the time being; he is closely following behind Takizawa Hideaki and Imai Tsubasa. You won't find a straight answer on this for a long time, unless something very unlikely happens.
did yamapi have a girlfriends?
i don't think so.... he has this contract which demands him to not having a girlfriend. that's what i heard...
ohh poor yamashita, not allowed to have girlfriends...T.T
I think he used to date Goto Maki when he was 15.
He also dated Abiru Yu, but I heard that they broke up.
last i heard, he was engaged