Often, when polyamory is something of a surprise, it's advised to slow down to give the mono a bit of time to adjust. This is VASTLY more important when it's introduced through an affair. Too many people make the mistake of trying to go straight from cheating to polyamory, as if now that things are "in the open", it's all fine. No. The biggest casualty of an affair is the trust and trust is vitally important if polyamory (especially poly / mono) is going to work. Wife and I made this mistake and it left cracks.
I think the next step should be trying to take a break and heal the trust between the two of you.