heartbreak

So...I was in a fwb situation (let's call him Robert) and it somehow felt more than that. We spent days together, cooking, watching tv shows. He'd tell me how good I look when I got ready for lectures and wait for me to come back and have a cuddle. We'd have nights when we wouldn't even have sex, just laugh and make fun of each other. Both of us were seeing other people as well, but for me it was just fun. No feelings or anything special for the other ones. Somehow, I fell for Robert. It was probably the fact that we were more than just shag buddies. We both have seen each other at our worst and our best. We've always been flirty, we've never been just friends, always more than that. A couple of days ago, he told me that we need to stop the fwb because he got feelings for the other girl he was having sex with. And now I'm alone and heartbroken and I have no idea what to do. He told me he'd miss me if we stopped being friends because we did have an amazing time together, and I know I'd miss him as well. I feel worthless, because he chose a girl he met 2-3 weeks ago over me, the girl who got him through his worst time for the past 4 months. I feel betrayed and not good enough, and most of all, confused. How can I have deep feelings for robert, and feel the way i feel around him, because he always treated me more than just a fwb, but he somehow fell in love with the other girl. What's wrong with me? What did i do wrong...