Depends?

threesome as in MFM or FMF

He might want to do it with another man and you, but maybe with another woman and you.

Maybe just role play it out without actually going through with it to work up his interest into actually doing it someday.

Maybe pick up another women and have the two of you experiment with each other while he watches. Then someday he might want to join in.

go slow and don't force him into anything.

most of the swinger websites are crap and full of men just showing their "junk"

but there are a couple of classy sites where you can find other couples with similar interest in your area.

Again, most of them are horrible and trashing.

find out why he doesn't want to do something like that. My SO and I have talked about it, but neither of us could do it. It wouldn't feel right for my SO. for me I wouldn't know what to do with 2 people, would my SO think I was simply wanting 'new meat' if I focused on the other person to much? would this make it easier for me to justify cheating? Would the new contact mess with my feelings and emotions? There are a ton of reasons why I would never want to do something like that. but thats just me. find out what bothers him about it, then you will know if a threesome is an idea worth pushing forward. see what I mean?

If you do not want to destroy your marriage and experience life eternal seperated from God then don't do it. In fact, Jesus said just lusting is a sin and just the thought requires repentance. Repentance means to turn from your sin and turn towards God. i suggest you read the bible start in the New Testament Mathew and then keep reading. Then start going to a bible believing church and learn about God.

I tried all the kinky stuff and reaped the consequences. I now attend a bible beleiveing church and have the best marriage imaginable. When we make love it beats the best sex I ever had. In my past marriage we did "everything". Its all empty and will not bring lasting joy. So for the good of your marriage and your soul REPENT!

If a woman wants to have another woman in bed with her husband, it is often because she doens't really care for him anymore. If she feels no jealousy at all at seeing her partner kissing passionately and stroking lovingly another woman, she really doesn't care for this man anymore. It's a fact. You just can't have a 3some with someone you love.
You are bored with him. If he falls for the other woman you don't seem to care. That can happen you know. I have seen too many marriages detroyed because of 3 somes.