dont be a pussy dude, just break up with her. y'know, "if you love her let her go" type shit. in my experience you'll never be able to convince someone to get help, they have to want it, and planning a wedding around mental illness definitely isnt going to do anything but make her more bitter about the situation. if yalls relationship is meant to work out, she'll get some help while you're in japan, you guys will reconnect, and maybe when you're both back in the same town you'll get a chance to rekindle the relationship. not to mention, if she really is the one, you wont move on from her. think of it like breaking up with your highschool girlfriend before going off to college, its just saving her feelings and sparing you of drama.(im toasted off my ass rn, if this doesn't make sense just ignore it)