Forever After This.

I can't remember this manga clearly because I suddenly started to remember this sad plot. Not clear if it is yaoi or shoujo but I would be calling them A and B.

A is dating B and recently there's a distance. B was seen talking on a phone very sweet, A heard about it and decided to see who B is going to meet up later on(they were talking on phone about meeting up). A saw B with someone(calling them C) holding hands or something (actions of a couple) A later confronts B when B comes back home, it was later revealed that B took C as A or something that relates to B's mind set. Like something was wrong or messed up and B mistook/viewed C as A and gave C affections that was intended for A. I don't think it ended happily, since I clearly can't even remember if it's yaoi or not.

Please help since I would love to know what happened. Also thanks for reading!!