Question

I've never been in that situation before. But most likely, I would just be a little upset, and still try to stay friends with her.

I'd stay friends with the guy/or girl . I'd still hang out with him/her , & maybe hang out with their girlfriend/boyfriend. Anthing could happen .

This boy I was TRULY in love with did this many times. I told him my real feeling,then he said his.{he was also in love} We started off being very good friends. NOT DATING! All the girls he dated HATED this so much. Same with all the boys I dated. We later started dating and still are.
My point is...tell him or her how you feel. Then become good friends and see how it would feel 2 date them.

Cry... burst into tears. Write something that sounds emo to express my feelings.

thats always hard, but, out of respect for them, I'd leave thier relationship be and try to befriend them,it's better than nothing