An equivalence relation is defined by three properties: reflexivity, symmetry and transitivity.
Doesn't symmetry and transitivity implies reflexivity? Consider the following argument.
For any $a$ and $b$, $a R b$ implies $b R a$ by symmetry. Using transitivity, we have $a R a$.
Source: Exercise 8.46, P195 of Mathematical Proofs, 2nd (not 3rd) ed. by Chartrand et al