Have you ever met someone and instantly you feel a deep connection with them, you discover similarities in your lifestyles, likes/dislikes, the way you think and act and you KNOW that you know this person, although it's the first time you ever met?
Sometimes there is an 'atmosphere' that feels charged, ripe with energy that you cannot explain. Sometimes it feels like you have known this person forever or they even feel like family to us.
It has been said that before we incarnate, we make agreements with certain souls for the purpose of exchanging energy, to learn from our experiences and sometimes to resolve unresolved Karma from previous lives.
These encounters can be wonderful or not so wonderful; of course when they are pleasant we are happy and enjoy the experience, however, when we feel that we are dealing with unpleasant situations we will try to move away from them. It is to our benefit if we work through them though and the learning experience we find will bring us to the next level of our life path. There is something that we have to learn/teach from/to each other and it is a valuable lesson for both people involved if we use the opportunity to grow.
We have 'soul'families that we 'agreed' to re-incarnate with but there are also unfulfilling or empty attachments when we feel drawn to someone in an unhealthy way based on some kind of a contract in a past life that is still tying us together; this is called a 'negative contract'.
The most important is to keep our compassion towards the other person, no matter if it is a negative or positive experience in our opinion, there is a reason for what is happening and we have our part in it.