Hey,
Trust me when I say I understand you. I feel the same way about my ex-boyfriend, and just the thought of him with another girl kills me. I can really tell that you love this girl, and I can't understand why she left you, just the same way I can't understand why he left me. She doesn't know what great guy she's missing, and some day she'll wake up and realize what she lost - and by then, you will have found a girl who appreciates you, who loves you, and who's always there for you. This is so much easier said than done, trust me, I know, but you just gotta believe in it. I feel bad for saying this, because I can't even manage to cheer myself up, but i truly mean it. Just wait and see.
xxx