It's that same triangle again. He, the girl and the other guy. This time its scalene-like. There is no questioning the affection distribution but a party gets more than the other. Do not blame her or call her clueless! She is human! Favoritism, careful consideration of pros and cons and so on, those are the factors. Ladies are planners, they go for what they think is right for them.
This is how it works! The luckless guy is the hopeless romantic, sending poems and love letters. He over pampers the lady, thinking the soft approach will pierce her heart but its all likely to be futile, the other guy is in charge. The other guy "freestyles" in the bowels of her heart, no stress or toil. He always knows she is stuck in his knot... Sad right?
Here comes the good part! The luckless guy could have an inexplicable change of fortune, the channel of affection pulls to his side and he suddenly becomes a believer in the "true love wins at the end" palaver .This rarely happens. This is the real world not TV.