carry a torch for sb

carry a torch for sb
hold a torch for sb
(to be in love with someone, usually without them realising this; esp. to suffer from unrequited love for somone) — быть тайно и безответно влюбленным в кого-то; любить тайно и безответно; любить без взаимности; безнадежно любить; быть безнадежно влюбленным; страдать от неразделенной любви
~ сохнуть по кому-л.

Example 1: Lory's been carrying a torch for Fred for years. — Она долгие годы безнадежно влюблена в него.

Example 2: Is it possible to carry a torch for 50 years? If you're still carrying a torch for someone, then the person you're longing for is probably long gone, replaced with a different version. You're setting yourself up for a disappointment because odds are the person won't live up to whatever expectations you've built up.
Often we're in love with the image of someone we've created in our minds. Not seeing the faults and flaws through the fog of infatuation and fantasy. At least that's what I would chalk it up to regarding someone who has carried a torch for a summer love when they were 15 years old.

Example 3: I got a message from this old boyfriend on Facebook that just said "Long time..." We sent some messages back and forth this past week and it became quite clear that he still holds a torch for me. He said he has thought about what went wrong with us and wondered if he did something to cause it. He wondered where I was and what I was doing.