Abandoned by My Fiancé, Chosen by Three Sirens

I thought I was teaching three beautiful mermen how to find mates. Instead, I made myself theirs. They weren't mermen. They were Siren triplets—and the three of them share one mate for life. Before I could escape, they dragged me into their underwater nest and chained me there. They won't let me leave until I'm carrying their babies. Then I remembered. Fifteen years ago, I had already met them. I made them a promise. I forgot. They spent fifteen years waiting for me to come back.