It looks like your guava tree is infected with anthracnose disease (fungal) caused by Colletotrichum gloeosporioides. It infects leaves, petioles, stem and fruits. On stem it causes dieback symptom, where the stem dies backward from tip of the branches (green growing tip will change to dark brown and then to black due to necrosis). It results in immature falling of leaves, fruits and young shoots.
On leaves, the fungus causes large, irregular dead spots at the tip or on the margin. This spot may become pinkish color due to spore masses.
On fruits you will see circular sunken brown to black spots which later enlarge as the disease progress. May also infect buds and flowers.
1. Remove the infected parts, plant debris and burn them.
2. Avoid overhead application of water and leaf wetting.
3. Spraying copper one or two times helps in controlling the disease.