Trust. We're talking more about love in the worldly sense here, because we can have Lovingkindness for people whom we don't trust. Trust, it's very difficult if we don't trust someone to have deeper communication with that person, because we don't really trust them, we don't want to communicate our vulnerability, our deeper thoughts. Therefore, there is a separation, a pulling away.
If that person does something, for example, they are not faithful, etc., then it's very difficult to trust them. Without that trust there's not a free flow of giving, a free flow of communication, and often comes that separation, that silence. So we don't become closer, which is the basis of good communication and the basis of good morality; in the sense that we don't trust their level of morality, we don't trust their level of compassion towards ourselves or others; because of that we keep them at a distance.
So that's what I mean about trust. Once trust is lost, it's very, very difficult to regain, unless that person who abused the trust makes that effort to be worthy of that level of trust again - and that may take some time. But as I said, we can have compassion for those we don't trust but we may not wish to be around them.