Look just be cool about it but be cautious. Ask your man hey what's your opinion on threesomes? then go from there, he might ask what do you think and you can say I'm curious about it, would like to try it out someday with you. 

If you're a christian and don't know what the Bible says, you're not a very devout one?  Maybe do your own research

1 Tim 3:12

Let deacons each be the husband of one wife, managing their children and their own households well.

You should only have sex with your husband and not with other people. It seems that you have some kind of sex addiction or you are bored with your current sex life. Maybe you can spice things up in the bedroom with your husband. Try something new.

Do you mean two girls to one man or two men to one lady. that is very important to know. 

Pretty obvious you aren't familiar with any religion, or you're trolling, take your pick.

Most religions that I know of have doctrine limiting sexual activity to one's spouse. To interpret doctrine any other way is cherry-picking to justify one's one actions.

If you want a religious perspective, ask your religious leader.

Every threesome I'm aware of where the female initiated it with introducing another female... the two women fairly quickly cut the husband out of the equation and ran off together. 

     I wonder if the third party is the pastor. Just kidding, sort of. The question is what are you willing to pay?  

     1. Exposure to a possible STD. That is a sexually transmitted disease.

     2. Your partner might like some alone time with your husband.

     3.You might like some alone time with the partner 

         You get the idea.

     4. Your relationship with your husband will change forever.

         Trust will leave on the next boat.

     5. Since love is built on trust then that is sitting in the rear seat.

     6. How are you going to raise kids with morals if you don't have them?

     7. How will you face the people in the church when this gets out. 

         Oh, it will, the Devil will see to that.

     8. It sounds like fun now but how will it hound you when you get to be 50?

     9. What comes after that when it becomes boring, swinging, or porn.

     I wish God would blow a loud blast with a horn when I'm about to make a mistake. But he doesn't. It is a still small voice that might say your husband isn't going to like this so don t even ask. I wish Eve would have wondered that when she ate the apple. Sin always takes you farther than you wanted to go and keeps you longer than you wanted to stay. Oh and the scars are long-lasting too.  Don't say you weren't warned. Grampa B   

From the bible as long as the third is your slave girl it is OK.  Do you have a suitable slave girl?  If not then you are probably thinking about adultery.  Or coveting someone else's partner.  Both of which are prohibited by the ten commandments.

the view would be that it is a sin to have sex with anyone you aren't married to