What should I do?! Advice Needed!

my ex husband & I are really good friends. We have quite a few mutual friends and go out together often. This weekend we went out with some of my friends (but he's hung out with them before) & closed the bars down. We all came back to my place afterwards and slowly people started heading home to call it a night. By the time I was ready to sleep my ex & my really good friend were the only two left at my house. He needed to get home to let his dogs out & she still wanted to party (they were both still tipsy.) They called and uber & headed to his house. Before leaving I had a conversation with him about not doing anything with my friend because that breaks the ex code & he assured me he wouldn't. He was coherent enough to understand what I was asking & saying to him. The next day I found out that my friend ended up getting suuuper drunk at his house & I immediately had a bad feeling about it. My ex & I had plans to paint my apartment that day so I went to pick him up. On our way to get some food I found out that him & my friend did stuff together. They didn't have sex but it's still upsetting. Due to my past with my ex (he cheated during our marriage which resulted in it going down the crapper because I couldn't trust him) I'm furious with him. I'm also incredibly hurt that my friend did anything with him as well because that breaks the friend code. Their excuses is that they were both really fucked up... 😒. Any advice would he appreciated. I don’t have many friends & cherish those that I do have so want to make sure I do the right thing.