Why do so many love poems in my languages prefer separation to union?

I'm new to formal philosophy, so please be patient with how I put this.

I translate between Malayalam and English, and I keep noticing that the love poems people treasure most are poems of separation. Kālidāsa's Meghadūta, where an exiled yakṣa sends a cloud with a message for his wife. The bhakti songs where the gopīs long for Krishna, who has gone away. Half the Malayalam film songs my mother sings while cooking.

In the rasa theory that goes back to Bharata's Nāṭyaśāstra, the erotic rasa, śṛṅgāra, has two forms: love in union (sambhoga) and love in separation (vipralambha). So the old theorists already treated separation as a kind of love, not as its absence.

My questions:

• Is longing (viraha) really a form of love, or a different emotion that only looks like love?
• Why would poets, and listeners, prefer it? Is it because union can only be described from outside, while separation is lived from inside?
• Is this something about Indian poetry, or about love itself?