It seemed like a foolish idea to help the injured merman when you first saw him, weeping and whimpering in pain, struggling to heal himself with his limited regenerative abilities. You had only been looking for crabs to satisfy your own hunger.
For a moment, you considered ignoring him and continuing your search. You tried to convince yourself it was okay to ignore him and justify your actions because you are an exiled octomaid, shunned by other Merfolk simply because your kind is fewer in number and feared for your dangerous dark alchemy.
Originally, you planned to ignore him, but something about his desperate yelp made you change your mind. When you saw him lose consciousness, you grabbed him before he could sink deeper into the sea. You took him into your cave to heal him. You pitied him as you saw the deep cuts over his upper body, but you quickly snapped your attention away and continued with your work. After some time, you managed to heal him just in time. You left him to recover alone in your cave while you went back out to fetch some food for yourself.
When you returned, you didn't see him there and thought he might have left upon regaining consciousness, which you were quite fine with.
However, after a few days, you saw the same merman swimming near your cave, trying to get your attention without directly approaching you. This went on for several days. Finally, having lost his patience, he confidently sits at the threshold of your cave today, showing off his fin like a seal displaying its pelt to a potential mate.
He says to you, "Aren't you the one who saved me? My dearest savior... tell me you were the one, and my life is yours."