Heartbreak and Loneliness: Dealing with a Sudden Breakup

I was in a relationship with this girl. we were trying to have kids and were talking about getting married.she started to talk to other people calling the friends then things went sour all of a sudden she broke up with me outta nowhere told me she didn't love me anymore. told me I wasn't good enough.she has since moved on to a relationship with another person. I don't know what to do she's forgotten about me and is completely ok and happy and I'm shattered into a million pieces and I can't seem to pick them back up to put my back together. I cry myself to sleep most nights. she was the one I vented to when I had a bad day or felt down but now that shes gone I don't have that. I don't have anyone.