Threesome

Amanda
My boyfriend and I are very committed to each other. We have been together about 2 1/2 years and our raising our children together. He are in a solid place and both really enjoy sex. 
We have casually brought up a threesome in the past but not sure if he took me seriously. I am very interested and want advice on how to bring this up to him. 
Also how do you choose another women to join?