What are the reasons for failed love marriage in astrology?

The main reason why a love interest may end up fruitless is due to the obstruction in the materialisation of love into a socially acceptable bond. A marriage bond.

In the Indian context mainly, This failure of a love relationship can be due,

1. Obstruction by parents.
2. Backing out of the partner.
3. OR backing out of native himself.

In spite of the fact that there are many reasons for a love interest or a long term love affair to end up in separation. For example, one partner's fate has a late marriage and another partner has destined early marriage.

Any reason it may be. There is some common pushing factor, in the breaking of these kinds of relationship. The marriage may be obstructed by partners themself or their parents or guardians. I list below the simple rule to identify them. The 5th lord and 5th house play an important role in flourishment of love may it be a love marriage or an arranged marriage. 5th house rules amusement, exciting things and productive ability. Love amuses, excites and is not only responsible for the productivity of offsprings, but also the productivity in life. YES! love can make you more productive in general. So for this love to fall out of life, 5th lord must be checked.

The rule goes like :

1. If 5th lord has connections with 6th house or its lord - the love partner of native can trigger the separation.
2. If 5th lord has connections with 12th house or its lord - the native himself can back out of love relationship.
3. If 5th lord has connections with 8th house or its lord - the obstruction can be created by parents. The parents of the native.

If more complex connections exist, then more complex becomes the reason for the failure of love marriage.