Failure At Life

So, I pretty much am a failure at life.
My life royally sucks. Want to know why? Because of my best friend, Bethany. She does things deliberately to piss me off, I swear. She constantly hurts my friends, so I don't know why I hang around her anymore. Advice, anyone?

The other day, we were sitting at the lunch table, and Mollie, Bethany's ex-girlfriend, but was girlfriend at the time, walks up and sits by me, and Bethany, being the smart ass she is, says, "Well, I think I need a new girlfriend." Immediately, I saw hurt and pain in Mollie's eyes. I, of course, slapped Bethany. But she just glared at Mollie. Later, I asked her what her problem was, and she said, "Well, I think I want to break-up with her."

Keep in mind, Mollie is one of my best friends. So I said, "Well, that was not the way to do it. That really hurt Mollie."

And you know what she did?! She shrugged and said, "Oh well." I gaped at her for a minute, then stormed off to fume by myself.

Later, she apologized to me, and me being the failure at life, forgave her. That's how my day went on Friday. Advice?