The Bhagavad Gita says that love and affection are the root causes of sorrow. What does that mean?

Swami replied: The love and affection on the worldly souls results in grief in some way or other differing from case to case. The ways may be: ungrateful revolt, untimely death, going out of the right path and falling horribly etc. The love to God will give you continuous bliss throughout the chain of births. Bliss is the infinite climax of eternal happiness without any trace of grief. But, grief (suffering) is the path to achieve that ultimate goal.