First, it cannot be your close friend. Why threesome dating sites are more and more popular, I think the biggest reason is that most people don't want to date their friends or someone they know, strangers can be the best choice of threesome dating. If you don't to ruin your friendship, I suggest you to date a stranger.
Second, date someone who can really accept threesome dating. If you want o enjoy the fun of threesome dating, you'd better date an experienced person who can really accept threesome dating.