I became friends with the other woman, how do I get out of it?

My boyfriend of 7 years cheated on me. It was 2 months long. The girl found my email and messaged me and we met up. We actually became fast friends in the process of me being angry with him. He has since apologized, gone to therapy and he wants me to cut the friendship off. She hasn't particularly latched onto me as she did in the beginning (going out all the time, phone calls etc). He says us being around each other gives him a "bad feeling". Also she doesn't know we are back together. She and I had plans for a girls night this weekend. He wants to take me away for the weekend. I'm loyal to him, but I think this might tip her off. What do I do?
I became friends with the other woman, how do I get out of it?
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