I know that I did not address in comments the many details brought up in the thread. Every topic was brought up with Barbie and Ken and discussed in detail. We decided several weeks ago to just be friends because all the nuances were complicated and stressful to discuss. Thinking about it and talking about it stopped being fun. The attraction didn't go away for any of us though.
Since getting to know Barbie better things have taken unexpected turns. Ken is not dominating anything. He is a special part of the mix but he is on the margins of what is happening between Barbie and I. We enjoy time without Ken.
I don't really talk to Ken unless we're talking about Barbie or sports. We are both happy not fooling around when she's away. He and I love each other but we are not IN love. We were platonic friends before I met Barbie and it feels platonic again even though we are having sex. With Barbie it feels like more than friendship. She is still nervous that Ken will leave her for me but she's more open with expressing her needs now.
Ken's roving cock is the same old story. He tells Barbie when he has been unfaithful. They are forgiving with each other about infidelity. We are using condoms and getting tested. I'm open to advice about sexual safety!