No, in your wife’s case it’s not possible to turn into a platonic relationship. She has a child with him (sperm donor or whatever she wants to call it) without discussing it with you first? You are tolerating her disloyalty due to her words of manipulation. When you tried to create a boundary she was blaming you saying “you have so much anger”. Of course you do, it’s normal to feel anger after what happened. She was belittling your feelings to get what she wanted. She still has romantic feeling toward that guy. I wouldn’t stay one more day if my partner ever did that to me. Respect yourself please. That’s how you outline a boundary.