The second, F & flee, some "boys" do that to avoid responsibility, to be free to sample all of the wares available, and other reasons I don't know about. My line of thinking is, F so it happens again and is an exclusive R.
In a weird way you are avoiding a certain amount of responsibility with that line of thinking. What if you were single and a woman you didn't know if you wanted to form a LTR with asked you for some beer? Women actually face similar dilemmas but it's more like usually women are the starting line-up then men play mid-game then the women take over again. The reason we have to play these kinds of games is that human beings aren't either fully monogamous or fully polygamous. My life would be a nightmare from h*ll if I had been bound for life to the first guy I had sex with. My life actually did pretty much suck because I was bound for 19 years to the first guy who knocked me up. There are decisions and choices to be made both before AND after you have sex with somebody or form a committed relationship. Whichever party is least suffering under a chemically induced delusion is the one who needs to take responsibility for making those kinds of decisions and choices.
"Tell me, what is it you plan to do with your one wild and precious life?" - Mary Oliver