He's a real piece of work. Between your post in this thread and your story, I agree with your stance that he gets off on being fought over.
That threesome the first night, sounds like it had nothing to do with you or his OSO, it's all about him.
Don't blame yourself. You're new to this and you were blindsided by his games, you really didn't stand a chance. He's manipulative and he's had practice at this. Somehow he's gotten this other poor woman involved in his games, and it doesn't sound like she's fairing much better than you did.
What's important now is that you learn from this experience. Trust your gut, believe in your rights, and don't let anyone pressure you into doing something you're not comfortable with or ready for.