Can we in Astrology predict if the partner has amorous tendancies and is likely to cheat on you?
YES, We can.
There are certain planetary alignments and certain factors that need to be analysed to make such a prediction. At the time of Horoscope Matching this analysis is very important to see how committed and loyal the person will be towards his marriage vows and his/her spouse.
*Rahu is the primary planet causing dissatisfaction in a person's mind and heart and makes you crave for more in every aspect-money, sex, love, everything.
If its posited in lagna (aspecting the 7th house) or in the 7th house itself(7th hs is for marriage and relationships), it causes multiple relationships.
*Moon rules the Mind and when thats in conjunction or relaiton with Venus, the planet for passion and love, induces people to look outside mariage for satisfaction.
*Jupiter, if weak in dignity or afflicted makes one disregard social conventions and moral limits and may make one cheat.
*The inter relationship of Mars(daring) and Venus(passion) if strong is also instrumental.
* The closer Rahu is to Moon/Venus, the greater the degree of chances of intimacy with another one.
*How strong is the Saptmesh? Is it strong enough to withstand the attraction, if indicated in the chart?
* Guru Chandal Yog esp in 7th house
On the positive side, if Venus/Moon comes together with Ketu, it creates a very loyal partner. He will have enough spiritual awareness to resist all temptation.
* Moon/Venus in relation with Saturn also creates immorality. Clashes in your relationship might push you into another's arms.
It would be judicious and sensible to actually look for such factors in the horoscope before finalising marriage. Also if one is aware that such alignments exist in his/her horoscope he might take steps by making mind and spirit strong enough to resist such temptations and make their marriage sweet and loyal.