सरुको हरफ - ब्राजिलियन पर्तुगिज - Eternamente serei sua.

There's nothing wrong with this request, it means Eternally I will be yours

Now it is ok, Thanks

Dear Lizz, one question of mine if I can. Is the subject feminine here? It's quite essential for proper evaluation.

Yes, it is feminine.

Thanks, dear!