[Sangetsu]

Walk away and find someone better. If she is still calling someone else her boyfriend, then she is either fooling with him, or fooling with you. Life is too short to waste time in such a relationship. Even if she does dump her "boyfriend", the odds are pretty good that the same thing will one day happen to you.

Don't be one of "those guys" who lets himself get strung along by some girl who is only happy when one than one guy is interested in her. Such relationships have high drama value, but the more time you spend in such a relationship, the less opportunity you will have to find and experience a "normal" relationship.

If you are in Japan, then you are know that there are plenty of beautiful and interesting women here, finding a good one isn't that hard (if you try).