Does a Chasan And Kalah getting married between Yom Kippur and Sukkos have to fast on their wedding day?
It is customary for the chassan and kallah to fast on their wedding day, and this applies even to somebody getting married between Yom Kippur and Sukkos.
Although these are days on which one does not generally fast, there is no prohibition on fasting (the days are not mentioned by the Gemara), and therefore the chassan does fast on these days.
However, in cases of weakness, one may be lenient.
Sources: See Mateh Efraim 624; Magen Avraham, cited in Mishnah Berurah 573:7.