Negro reply, but I agree with you. This is the folly of all the “best/closest friend” in not just yuri, but media in general. I see it all the time in yuri manga. The best friend is secretly in love with the MC but is too scared to take the last step out of fear of rejection and fear of ruining the relationship they have. Then before they realize, it’s already too late and the person they love has already found someone else.
It’s heartbreaking too see, honestly. However, at the same time it’s also part of youth to experience such things. Thankfully some authors aren’t completely heartless and allow for these characters to eventually do find love of their own.
All to say, I feel so sorry for Sayaka that her first love was that bitch that just played her. Then her second love will always be unrequited. But I do like her character and I hope for a happy outcome for her.