I'm lucky that my boyfriend is pretty supportive of me going, and we've been together long enough and have a steady enough relationship to be able to survive a year apart, I think.
I keep hearing about people going to Japan on JET or other things without any Japanese and coming back without learning much either, so I'm sure you'd do fine
In all the places I went to in Japan they either spoke some English or we got by with my crappy Japanese and charades. It definitely sounds like it would be a lot easier to get by and make friends with some Japanese though, and people always seemed to appreciate my bad attempt at their language all the same.