How can you fall out love with someone over night?

My boyfriend of three years broke up with me last weekend. It was so shocking and unexpected. Just the say before he was telling me how much he loved me and how I was his world. Then the next thing I know he broke up with me via text message! He said he didn't love me anymore and he was cheating on me. I have been trying to contact him and begging for him back like a fool. I just don't know how to live without him. He wasn't just my boyfriend, he was my best friend, and pretty much my only friend. I feel lost without him. I can't really sleep...When I do finally fall asleep, I dream about him and end up waking up and then I can't fall back to sleep. I can hardly eat. He's all I think about, and all I keep doing is going over things in my head and blaming myself. Everyone tells me that it's normal to go through heartache, but I can't look at it from that perspective. I know that I have not been a great girlfriend at all times, I have issues, but how can you go from loving someone so much to not loving them at all within a 24 hr period? If love is that unpredictable and can end that easily, then whats the point? How can your feelings take a 180 overnight? He is about to be 28 yrs old so its not like this was some young juvinille relationship.