Venus is the ruling planet (karaka) for males while mars if for females regarding "desire".
More than one marriage or liason is usually exhibited by the house itself,the locations and position of 7th house lord,association to 7th house,aspect upon the 7th house,navamsa occupied by 7th Lord,Upapada-8th H,Jaimini dara karaka are to be referred in addition to house number 5 and 12th which relate to affairs and place of sleep respectfully.
Sometimes the moon or the sun horoscope answers better than the traditional ascendent chart.
Book,if any, may help only in the limited sense,for me,astrology is more an intuition than bookish knowledge.
The poet says "Zindgi kya hai
Hata kar Dekho"