The subject of separation or Divorce is dealt by almost all old scriptures including Brihat Parasara Hora Sastra, Bruhajjataka and Phaladeepika
Here are some of the combinations for it.
1. Separation may occur if 7th lord is placed in 6th, 8th or 12th houses and is in conjunction to malefics
2. Separation may occur when 7th house lord is debilitated or 7th lord is in close conjunction with Sun.
3. If there is combination of good and bad planet in the seventh house, then separation is indicated
4. If Venus or Mars or 7th lord is hemmed between malefics, or is in conjunction with malefics.
In this context, 7th Lord conjunction with malefics is more important than 7th lord aspected by malefics.