Why "naše rodiny se nenavidí" (if I remember right other task), but "často si píšete"?
Some verbs take the se form, others take the si form of the reflexive. The si form is dative.
Compare, for example:
"Jak často si píšete dopisy?"
(Please correct my sentence above if it is wrong.)
I wrote: How often are you writing to each other. Why is not this solution correct?
For habitual action English uses the present simple tense.
Is the 'to' in 'write to each other' necesary?
It is accepted without.