The rules of casual sex...

Who doesn’t get a pang of… something – surprise, jealousy, betrayal – when they hear about someone they’ve recently been with now getting it on elsewhere?

Blame it on La Niña or the return to popularity of Strictly Ballroom classic "Love Is In The Air" (at least in my mind) but it seems the majority of my mates - both male and female - are experiencing flood-like conditions of late in their love lives.
This is good news. I approach Anthony Robbins levels of willpower when encouraging my mates to engage in bedroom calisthenics. However, something went amiss over the weekend. I saw Jill, a female mate and lifelong friend who considers herself the Blanche of her Golden Girls circle of mates, walking through my suburb clearly still on a date that had begun the night before (the hair, unless she was months early for commemorating the anniversary of the untimely passing of Amy Winehouse, gave her away). Passing with little more than a quick hello and a shared look that said "the next time I see you we're doing a rain dance to Toto's 'Africa' to celebrate the wet season" I continued on with a female friend of mine in search of a Saturday morning sausage roll (don't judge, it was a long weekend and I've got a great local bakery). As we took our tastebuds on a trip through pastry nirvana, my breakfast buddy commented, "So…looks like Jill had a good night. Didn't she hook up with your roommate Dave last week?" Consumed with a sense of loss over my rapidly disappearing piece of mystery meat heaven, I offered up a nod of the head and a grunt which was intended to communicate "why yes, I believe they've been on a date or two and she stayed the night last week. Good spotting" but could have been interpreted as a pig snorting at an empty trough.
The fact that Jill had done the no-pants dance with my roomy last week and had now committed sins of the flesh with another bloke didn't worry me. She was just going through a hot streak; think Madonna circa Confessions on a Dance Floor. This would inevitably taper off. My breakfast pal wasn't satisfied though; it wasn't that she was anti-getting-jiggy-wit-it (both the song and the act. How could anyone hate some family friendly Will Smith rap?) but there hadn't been a final act in Jill's dalliance with my roommate, they talk regularly and there seems to be a mutual interest. If she's still actively seeing one guy - albeit with no official title or commitment - how could she be bed-hopping without first cutting loose my Dave? This happens more than I'd venture most of us would like to admit. Who doesn't get a pang of… something - surprise, jealousy, betrayal - when they hear about someone they've recently been with now getting it on elsewhere, no matter how illogical the feeling may be? It happens, sure, but nonchalance is hardly par for the course. So what's the guide for a situation like this? If I've been with a girl and there's been no talk of any type of exclusivity I don't have a problem with it as long as it's not flaunted in front of me. Am I wrong; should be there a cap on dates, a degrees of separation agreement or some sort of friend-sharing deal so there's no awkwardness when exploring other options?