One of the couples in "Links" is kind of like that. "Escape" is a twisted version of this. "Kimi ga Koi ni Midareru" was a little bit like that (both men are in love with someone else, but start to love each other). "Interval" is similar, but it's only one guy who has another love interest.
plz suggest any other similar manga but they end up with each other instead of their love interest .......thanks