Most of our relationships are organic and we rarely sit down and think what we're getting out of the relationship. Sometimes we're together with someone just because of familiarity even if it is toxic. On another note when asked we tend to not be able to say why we like someone because usually the reason is the sum of 1000 little things. Those 1000 things are what our subconcious thinks we need at that point in time.
Another thing to note is, each relationship has an ideal proximity. Getting to close to a certain person might be disastrous. We can share a certain part of our life with someone and not other parts. For example someone we get along very well with might not be the ideal housemate or business partner. Someone we love might not be our ideal companion.
This practice increases our skills in surrounding ourselves with the right people at the right level of proximity.