"I love my girlfriend."
Translation:Εγώ αγαπάω το κορίτσι μου.
It's included in the alternative translations, although kind of far-fetched.
None, they are simply alternative forms of the same verb. Please read the Tips and notes here https://www.duolingo.com/skill/el/Verbs%3A-Present/tips-and-notes (section: CONTRACTING VERBS).
Is "Εγώ" strictly necessary here? It marked my "Αγαπάω το κορίτσι μου" as incorrect!