fall out of love
To gradually lose the deep feeling of love (for someone or each other) in a romantic relationship until it is gone. Modeled on the phrase "fall in love." Nothing dramatic led to the end of our relationship—we just fell out of love with each other. I'm terrified that we'll fall out of love if we have to spend so much time apart.
fall out of love (with someone)
to stop being in love with someone. She claimed she had fallen out of love with him. He also had fallen out of love.