Is a kohen allowed to marry a woman who had relations already? if yes, what about if it was with a non-jew? Lastly, what if the relations had with a non-Jew was rape? Does that still count her out for a kohen?
It is permitted for a kohen to marry a woman who has already had marital relations. However, it is not permitted for him to marry a woman who has had marital relations with a non-Jew. This applies even if the case was a rape.
Sources: See Even Ha-Ezer 6-7.