It is the suffering of ambivalence: the murderous alternation between bitter resentment and raw-edged nerves, and blissful gratification and tenderness
To have a body is to suffer. Does anyone with a body know peace? Those who understand this detach themselves from all that exists and stop imagining or seeking anything. The sutras say, "To seek is to suffer. To seek nothing is bliss." When you seek nothing, you're on the Path.
A very weighty argument is this namely, that neither does the light which descends from thence, chiefly upon the world , mix itself with anything, nor admit of dirtiness or pollution, but remains entirely, and in all things that are, free from defilement, admixture, and suffering.
The rationale for loving others is the recognition of the simple fact that every living being has the same right to and the same desire for happiness, and not suffering, and the consideration that you as one individual are one life unit as compared with the mulititude of others in their ceaseless quest for happiness.