Like in Zig Zag Don, where...
Spoiler (highlight to view)
... the female lead has a one-night stand with her best friend, followed by a tortured no-strings and eventually with-strings relationship, but in the end decides to be with another guy who loves and values her more (and whom she also grows to love after breaking up with the so-called "friend"). I think the friend's a bit of a sleazebag, actually; he seems to think women are basically sex objects. Augh.
Or Hotaru no Hikari, where...
Spoiler (highlight to view)
... the protagonist has a full-on relationship with the younger man, with genuine love (and, obviously, desire) on both sides - however, that relationship doesn't last and she discovers a much more real and stable relationship with her older boss (not through any fault of the first man, I'd say, but rather because she's learned more about herself and what her actual needs are).
Manga like that, please!
Oh, and...
I'm looking ONLY for shoujo, josei, BL or GL manga! (NO shounen, seinen or hentai, please.)
Thanks in advance!