carry a torch for (one)
To be in love with one, especially secretly and/or unrequitedly. I've carried a torch for her since high school, but I've never been able to tell her how I feel. Susan carried a torch for him for years after they broke up.
carry a ˈtorch for somebody
be in love with somebody, especially somebody who does not love you in return: She’s been carrying a torch for him for years.