Is it okay to walk away from a friendship?

My friend let me down in a big way. He was supposed to be best man at my wedding but now it's cancelled. He never told me if he was coming and then he said he wasn't able to come. I asked him to be my best man 2 years ago and he said yes. He was supposed to organize the bachelor party and make the speech but he didn't even tell me if he was coming or not. He never even reached out and said he couldn't make it. His sister is getting married in 2 months and I have no intention of going.