If your bf is only interested in sex with others and you want an emotional connection then I would not consider this scenario together. I would stay well clear of any threesomes like this. Maybe go swinging to fulfil his desire, if you can pull that off. I wouldn't be able to, but maybe you can.
There is a possibility that someone would get hurt. She might be like you and want a connection or she might be like him and want sex. Either way, you could get hurt because your connection will deepen and they will just be confused and dismissive of that or he could get hurt when you have sex a couple of times and she becomes more interested in spending time with you alone or falls in love with him and he has to tell her "look hun, it was just sex."
I would be negotiating you exploring a relationship with her alone. There is no reason he should be involved. He might be disappointed but that will be shorter lived and cause less havoc than the alternatives I have mentioned above.
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