Indeed, sometimes Kṛṣṇa puts them into extreme suffering by separating Himself from them. Nonetheless, they cannot forget Kṛṣṇa. When Kṛṣṇa left Vṛndāvana for Mathurā, the gopīs became most dejected and spent the rest of their lives simply crying in separation from Kṛṣṇa.
Nectar of Instruction, sloka 10 - Purport(Excerpt)
