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Re (from SusieHomewrecker, Post #3
"When we had the opening up discussion, I did specifically state that I would be comfortable with him sleeping with her on his own. The issue that arose however is that it happened in February, and I only found out a few days ago."
Can I ask, when did the opening up discussion occur? In February or more recently ... Was it after he had already slept with her (on his own)?
It sounds like you guys have some obstacles to overcome, but you've already made considerable progress by opening up the channels of communication. I hope Polyamory.com will prove to be a helpful resource to you. Certainly there is a wealth of info to read up on here, and you can interact with other members to get thoughts, advice, support, etc.
Glad to have you aboard.