Translation - Greek-Latin - Είναι ο φίλος σου, ο σύντροφός σου, ο προστάτης...

Feminine option:
"Ea amica tua es, socia tua, protector tua, canis tua. Tu vita eius es, amor eius, ductor eius. Ea tua erit, fidelis et devota, usque ad pulsationem cordis sui ultimam. Debes dignus esse tanti studii".

Based on a following bridge of User10:
"S/He is your friend, your partner, your protector (guardian), your dog. You are his/her life, his/her love, his/her leader. S/he will be yours, faithful and true, till the last beat of his/her heart. You ought to be worthy of such a devotion."