So, you're both married and cheating on your respective spouses.. Then, you initially told him you wanted to be friends but moved on to making out with him.

You ask how to avoid suffering more? A messy situation such as this one will only involve pain. You are moving too fast with someone you don't even know and who is already 'taken'. As you wrote earlier on: "I know almost nothing about him". Plus, him cheating on his wife and never even acknowledging her speaks to his character.

All of these won't make for a healthy, pain-free, relationship.