Some context: I (22M) have been friends with a girl (23F) and a guy (28M) for about 5 years now. 4 years ago me and girl had a romantic relationship together. It didn't quite work out, but she insisted that we remained friends. I was hesitant at first, but over time it seemed to work out just fine, and I really valued the friendship we had developed. I recognize most people don't have this experience, and perhaps that's for a good reason, as you'll see later. 

My guy friend recently has become interested in dating said girl. He was very respectful about it - even asked me if I would be okay with it, because he didn't want to step on anyone's toes. I said yes because I know both of these people - they're both friends I've had for years, and I thought I could trust them.

Well. I trusted wrong. The guy friend told girl that if she wanted to date him, she'd have to massively cut back her relationship with me. And while he didn't come right out and say it, I can read between the lines: he doesn't want me to have a relationship with her at all. And I guess she agreed with him, because she cut off all communication with me entirely.

I was homescholled my whole life. I had no social outlets growing up. So when I left home for college, the friends I made were more or less the first friends I'd ever had. I don't have a wide net of friends either; I could probably count the number of friends that I actually talk to on one hand. And these people were definitely on that hand. So this happening is devastating for me.

Essentially it shows me that my friendship isn't valued in the slightest. That at the drop of a hat, these people are willing to completely write me out of their life. And that makes me really sad.