Dream about affair with brother in law refers to your need to be more cautious before proceeding on to new situations or adventures. You are feeling unfulfilled in some aspect of your life. You are not taking or accepting responsibility for your actions. It is a clue for your negative emotions. You need to find a way to get out of a rut.
Affair with brother in law dream is an indication for a lack of self esteem or self confidence. Emotions that have been suppressed into your subconscious are becoming too overwhelming to keep inside any longer. You may be contemplating on strengthening and changing aspects of your character. This dream is a message for a lack of trust. You have not analyzed a situation long enough or that you do not want to deal with the problem at all.
If you dreamt about affair with brother in law:
New trends that you have been enjoying lately may not be all that they are cracked up to be. Now is the time to mentally go back and review. It seems that you have skipped over something too quickly. Revisit your ideas. Are they truly sound?