As long as I got pregnant with the child of a warlock before my previous child died, I would remain powerful and young. That's why I summoned you to Santo Domingo. I felt you...a drift in the ocean. So I used my powers to bring you close and I spelled you so you would fall in love with me. I needed you, mi amor, so that I could live.
This is the relationship between Eva and Killian Gardiner. Killian met Eva when he woke up on an island. They began spending a lot of time together and eventually shared their first kiss. It was Eva who showed that Killian was a warlock. They eventually consummated their relationship. When Freya Beauchamp comes to the island to visit Killian, she finds out that they got married. It is most likely Eva spelled him, but it was shown that Eva gave him what is believed to be a love potion. She also practiced a ritual of fertility, finishing it saying "You are gonna give a baby". It is not clear also if Eva is the owl of omen, or protection.
However, because of the potions, they are in love, married and happy together, but after a few episodes she reveals her true nature to him, which was that she needed him to impregnate her otherwise she would die of old age. She really loved him, but he didn't return those feelings of love.When he wasn't spelled he did not reciprocate those feelings of true love.