Similar to how you test drive a car before puchasing it. You have sex with someone before marriage or before you get too serious, in order to ensure you are willing to stay sleeing with the same person for what could potentially be the rest of your life.
guy1: "How you and Jenny doin' bro?"
guy2: " I dumped her"
guy1: "What? Why? I thought you really liked her"
guy2: "I did but I took a sexdrive and that pussy was in worse condition than a rebecca black video"
guy1: "You did the right thing"
girl1: "Did you here Cathy dumped Erik a month before the wedding?"
girl2: "Yeah, she finally took a sexdrive and let's just say steriods were in his recent past"
girl1: "She did the right thing"
Like a real Affair, a Facebook Affair is when someone is cheating on their boyfriend/husband or girlfriend/wife with someone on Facebook. The relationship never really becomes physical and the two people might never actually meet. The Facebook Affair ranges from them sexting eachother and having very sexual conversations like they are a couple, to flirting and giving eachother "cute" nicknames like "honey" and "boo".
This can go on for months or be a one night thing. The two people may actually know each other or be complete strangers, but either way when the person they are actually in a relationship finds out there will be hell to pay.
Jack: Hey, did you hear Bill got fired?
Mike: What? Why?
Jack: He was having a Facebook Affair with his boss's wife. She left her profile open and he saw their messages.
Mike: Damn, but she is a milf sooooo...
Jen: I feel terrible.
Kelly: What happened?
Jen: Mike and I had a fight lastnight and I got drunk and had a Facebook Affair with an Italian Underwear Model.
Kelly: Damn, but Marks a douche sooooo...