What does the Gita say about the death of a loved one?

अशोच्यानन्वशोचस्त्वं प्रज्ञावादांश्च भाषसे ।
गतासूनगतासूंश्च नानुशोचन्ति पण्डिताः ॥

aśocyān anvaśocas tvaṃ prajñā-vādāṃś ca bhāṣase
gatāsūn agatāsūṃś ca nānuśocanti paṇḍitāḥ

You have grieved for those who deserve no grief, and you talk words of wisdom. Learned men grieve not for the living nor the dead.

देहिनोऽस्मिन्यथा देहे कौमारं यौवनं जरा ।
तथा देहान्तरप्राप्तिर्धीरस्तत्र न मुह्यति ॥

dehino 'smin yathā dehe kaumāraṃ yauvanaṃ jarā
tathā dehāntara-prāptir dhīras tatra na muhyati

As in this body infancy and youth and old age come to the embodied self, so does the acquisition of another body; a sensible man is not deceived about that.

अव्यक्तादीनि भूतानि व्यक्तमध्यानि भारत ।
अव्यक्तनिधनान्येव तत्र का परिदेवना ॥

avyaktādīni bhūtāni vyakta-madhyāni bhārata
avyakta-nidhanāny eva tatra kā paridevanā

The source of things, O descendant of Bharata, is unperceived; their middle state is perceived; and their end again is unperceived. What occasion is there for lamentation regarding them?

मात्रास्पर्शास्तु कौन्तेय शीतोष्णसुखदुःखदाः ।
आगमापायिनोऽनित्यास्तांस्तितिक्षस्व भारत ॥

mātrā-sparśās tu kaunteya śītoṣṇa-sukha-duḥkhadāḥ
āgamāpāyino 'nityās tāṃs titikṣasva bhārata

The contacts of the senses, O son of Kuntī, which produce cold and heat, pleasure and pain, are not permanent; they are ever coming and going. Bear them, O descendant of Bharata!