Just in case the title of this post is sending you on a wild goose (thought) chase in a particular direction, this is not a post about infidelity. It's a post about 'the other guy'. Glad that cleared things up *grin*
See, I'm currently reading The White Road (Lynn Flewelling). *thinks* Yes I'm invested in the two main characters and what happens to them, but...it's another character, a secondary character, that has me biting my lip and..wishing (fervently)..for his safety and, ultimately, his contentment. (He's been through so much I'm not if he can be truly happy, but if he could be I would like him to be.) If something happens to him (something bad in other words) there will be letters (to the author). Oh will there be letters! Because...sometimes I just need to believe in happily ever afters. Does that make sense?
So, have you ever invested in 'the other guy' more than the main character(s)?