Hope you don't mind me chiming in here as my husband and I were discussing this same thing tonight You have to be completely comfortable in your relationship, completely in love with your husband/SO, totally trust them before you bring someone else in. Before I got married I dated a guy off and on. I have a girlfriend I used to hook up with. I decided to have her come and join us for my then boyfriends birthday. I wanted her for me only and I did not want HIM to do anything with her. The first time all was well....I just wasn't comfortable with him doing her. He kept asking and asking and asking. We eventually broke up. My friend ended up getting married as did I. After a while we started getting together while our husbands watched, moving to separate rooms when it came time to have sex with our husbands. It progressed to having sex in front of each other...still just my girlfriend and I hooking up...it finally came to swapping. My husband and I just a few hours ago were talking about bringing in another girls (single) and I really surprised myself saying it would be totally ok with me for him to do the other girl (in fact we are talking about going to a swingers party). My ground rules are: no getting her phone number (If I wanted to see her again, I would do the hook up) no chatting with her online, on the phone, no lunch dates, no seeing her without me.....for us we separate a good f**k from the times we make love. I am completely comfortable in the fact that he loves me and we are a family and I would not want him to hook up without me. If he ever crosses that line, we would deal with it at that time. (Weird thing is we did do a threesome with one of his guy friends and my husband was the one that initiated it and told his friend to do me...asking me first) so i figured I owed him anyway...my advice...go for it only if you can separate a f**k from love making and make sure you are totally committed in your relationship