There are too many unknown variables in this scenario to predict exactly how I'd handle it, but I would do everything I could to try to save both, and I would not factor in love when determining who to go to first. I'd assess the scene and go for the one who was in most imminent danger of drowning. If it was likely that that person would drown before I got to them, I'd go for the one that I could save. Then I would set sail in search of love of the requited variety because neither of these people are right for me.
Just to make things a little bit more easier for everyone to answer. Let us say that the person you love is your girlfriend/fiance and the one who is loving you is your best friend. Would u still stick to your original answer or choose one lf them?