A knight is dragged into a satanistic orgy that is aiming to create antichrist

I remember i read this book about 10 years ago, about a young knight. It first was describing a crusade, the hardships of it and how the knight gets wounded and has to go back to europe(that might be another book completely tho). In that city, he falls in love with a noble(?) woman. He finds some friends there too, and ond of his friends invites him into a nearby castle, which turns out to be a place where a small circle of satanists host orgies. On of the saranist women can take on appearance of any other female, from cleopatra to the love interest of the protagonist. He spends some time there against his will, but yhen of the satanists has mercy on him and lets him go.
Memories of this book had been bothering me for some time now, and i tried so many search engines and still couldnt find it. If you happen to know the name of this book or something remotely close - please reply.