My personal top picks for novels with the “Light of my life” trope where one character saves another (literally or figuratively) and is the main source of warmth in their life. This could be one-sided or go both ways. 

I like stories that delve at least somewhat deeply into this and explore how much the characters mean to each other. What would have been their fate if they’d not met or how deeply do they struggle without the other’s company? How strongly do they yearn for that light?