Your discomfort and uncertaintly about being friends is certainly understandable. I encourage you to trust your feelings. You have experienced a huge betrayal. Your ex-husband is not understanding how his lying has hurt you. If he can not respect your need for space right now and his need to repair the trust he has ruined, he will not be able to be a respectful friend. You need to surround yourself with people who respect you and validate your feelings. Why do you feel like you owe him anything? You can not be his friend right now, move on, get healthy, you deserve it.
Take some space from him, it is clear that you are hurting. Get into some therapy for yourself. Heal. Find new friends. You need to focus on you. Stop focusing on him. The best way you can get him to understand and is to tell him you can't be friends and stop having contact with him. You have not been able to get him to understand you thus far, I think he doesn't really care what you think or feel.
I do not know where the responses go, that is a good question. I wish you the best!