You're having fun at this point and you promise yourself that you won't, under any circumstances, become attached.
You're lingering at your FWB's house for longer and longer and now, the two of you have extended activities from purely hooking up to actually talking and hanging out.
This keeps happening until one day, you wake up beside this person, look over and start to freak out because you realize you genuinely like him or her.
Maybe your last relationship was a disaster and this arrangement was only supposed to be a short-term thing.
Maybe you recognize you're falling for emotionally unavailable people because you're emotionally unavailable yourself.
Ideally, of course, your FWB returns your feelings, and both of you want to take the arrangement to the next level.
More often though, your FWB doesn't return your feelings, and the house of cards the two of you built together so precariously falls apart.
After all, if your FWB were the type of person who wanted to be in a relationship, wouldn't he or she be in a relationship already?
You two may still meet every once in a while in order to relieve some sexual frustration, but once you admit your feelings and get rejected, nothing is quite the same.
You never have to feel guilty when you're flirting with other people or lazily flicking through Tinder.
There is just one unspoken rule: You two have to keep it this way for as long as possible.
You're probably recently out of a relationship and emotionally unavailable, but you're also sexually frustrated.