I think its like any relationship. You have consequences, with swinging, usually you've found a couple to be with and that's fine, they are together, in love and happy it's just a night of fun and crazy sex with another couple. With a threesome, you are inviting someone into your relationship. I personally couldn't handle someone touching my bf, but that's just me. Its a personal choice, I have friends that have threesomes and they say its exciting and fun. I guess the only way to know is to have one, be sure that you are ok with it and that in the end, you will be happy with the outcome.