Question Is there a halacha that says a person who converted to authentic orthodox Judaism cannot marry a person with whom they met and had a relationship before and part of during the conversion?
Answer Not that I am aware of specifically. However, an Orthodox Jew is not permitted to marry a Gentile (or another Jew who is not Orthodox), so unless they converted to Orthodoxy as well then the two could not marry for that reason. Certain individuals (ie Kohanim) cannot marry a convert. Hope this helps. Shabbat Shalom!