Or is this game bordering on hentai?

I mean implied masturbation scenes, breasts in the shower....

I think the dev team need to get a cold shower.

It's definitely a mature age game.
There's sexualized content - whether you consider that "borderline hentai" would depend on subjective opinion.
Whilst it's there, I don't feel that it's excessive.

Some people feel uncomfortable (or offended?) around sexualized content. Personally I don't mind it and see no problem with it. If anything, I'd be much more disturbed at the various other themes (violence, hatred, poor treatment to children etc) than anything pseudo-hentai.