How do i help my Fiancé with his anxiety? It's making him physically ill

Here's the background. He had to ask his best man to step down. We talked about it a lot because he would come home from work upset ALL. THE. TIME. They have been friends for years before they worked together. This year he noticed best man kind of falling off the wagon. Coming to work hungover, coming to work late, leaving work early, picking fights... he eventually asked my Fiancé to carpool and he made it sound like this awesome thing and he'd save gas. It was NOT awesome. My Fiancé is a recovering addict, he's been sober for 9 years! He knew what was going on and started to feel uncomfortable with the whole idea.... then best man got fired. Didn't talk and wouldn't answer my Fiance's calls for 2 months! Then he called him and they were able to talk... things were fine until he had to tell best man he had to step down and why.... now "things aren't going to be the same between us", "I didn't know you guys had such golden standards", "I had stuff planned and my speech written", "so much for loyalty", "you really can't trust me?".... just making my babe feel awful... which he already felt awful to begin with. My Fiancé told him that he has other things he needs to focus on and he meant everything he said with love. It's been really bothering him and I just wish there was something I could do or say to help him get through this. I'm at a loss, I've never seen him so anxious before.