It is a pity that such a situation happened to you. I understand you're upset, but don't blame yourself. You trusted him, but he just doesn't rely on your trust. Because he's an idiot.
I think he has behaved badly enough, so you should not continue to communicate with him. Even if he apologizes very much and you forgive him, you have to remember that he will not change and will behave the same way.
You're really right that it’s a bad idea to be friends with your ex. Especially if the relationship did not end well.