∠ 1+∠2 is equal to 180, that is, ∠CDB=∠ 1, so CF//AE (isosceles angle is equal).

Also, ∠ DAE = ∠ BCF, so ABCD is a parallelogram. So ad//BC

DA divides ∠BDF equally, so ∠FDA=∠ADB and ∠FDA=∠C=∠CBE, ∠ADB=∠DBC, so ∠DBC=∠CBE.