There is pure love and impure love. The difference lies in possessiveness or release. Pure love is the root of lasting happiness. Impure love creates only suffering. Impure love that is tainted by the ego and possessiveness leads to jealousy, then anger and finally separation. Pure love free from possessiveness leads to harmony and peace and may even transform a negative companion. A relationship then becomes a Bodhisattva activity. 

Someone, who has understood the nature of mind, will even take on a negative companion, as one has understood that negative emotions are temporary; they come and go. That disturbing person's mind and one's own mind essentially are the same. What stays throughout lifetimes as the seed for happiness is pure love. Thus, when one truly understands the nature of mind, samaya commitments cannot be broken. Even if it happens that one quarrels, this temporary occurrence never moves the ever-prevailing love. 

If one does not understand the nature of mind, one will cling and try to possess. We then are nice to those who are nice to us, but not nice to those who are not nice to us. This love is impermanent; it cannot last. 

Pure love will always last. And my love for you will always last.

-- Garchen Rinpoche