How to Deal With a Broken-Crashed Heart that already broke into pieces?

I'm writing this in a gloomy wednesday with Brandy's Brokenhearted as a backsound. Sometimes I just really dont know what is going on, right now. I have no idea for what already happened. Everything's just happened really fast. Knowing that your partner have an affair with someone else: really break our heart. I cried every wake up and before go to sleep. Or even in a random situation. It feels like all in my head is just about them, (was) having fun behind me. Ive learned before: not to give 1000000% heart to any person. Never really giving all my heart because im afraid to fall and to be cheated. Aaanndd yes, I've been cheated several times by some boys but yeaa I never get hurt. It's just funny how they get hurt and cry when I left them. And i'm giving a very wide smile to em because i didnt feel any pain at all. But it's just different. We're about to marry in less than a year. And i think it's my time to give all my heart and all my life to a boy that i already choose. I never-ever-ever think that he will cheat on me. Possibility: 0%. BBUUUTTTTT....... he did it. Seeing how he flirt on her (anddd so did she) just driving me insane. I wish I could die right now. I wish he kill me instead. I wish I could just cut my own radialis artery just because it feels like I couldnt living any life anymore. Life is really bad to me. I didn't do anything wrong. I never did anything wrong. But why people keep did something bad to me? Why waking up in the morning really feels bad.. I wish I could close my eyes all the time. I'd rather feel nothing than hurt.