Is it better to invite a stranger or a fwb for MFM threesome?

My BF(35M) and I(27F) have been planning to have our first 3some. It’s the first time for both of us, and I am hesitant about finding a stranger. So I approached a trusted previous fwb, who agreed to do it with us. But I can clearly sense his reluctance, because he might feel objectified and downgraded (from a date to a tool). Now I am having second thoughts about the 3some, and wonder if I should find a stranger instead?