Apparently the problem is in not in the game itself, but in the translation patch. It messes up the event triggers in some way.
Things already seem to be going wrong at the part where you get to choose whether or not you want to go on a date with her - no matter what I choose, the date proceeds anyway. Then a little while later comes the bad end.
Though judging from Hones' walkthrough, the problem could also be that the Save Her/Don't Save Her-choice isn't working as it should. Maybe it fails to trigger a "You Saved Her"-flag no matter what you choose, thus railroading you towards a bad end.
There is a fix for this this problem out there, but as AMagicMan already said, all the links to it are dead. All I can find are MediaFire uploads that expired years ago, and TLwiki isn't any more helpful either.
The best solution I can think of is play the untranslated Japanese version, make saves after the choice scenes, and see if you can copy and load those into the translated version.