I'm a dude, so I don't know if my thoughts will help, but I can't do Friends with Benefits. To me there has to be some kind of spark (chemistry), and that doesn't come to me easily.
I'm 44, married, kids, etc. (very typical middle class family) and am introverted, so I didn't hook up very often when I was young.
I very much wanted sexual experience from about the time I was twelve or thirteen and was crazy about girls beginning in the sixth grade (I still remember the butterflies holding hands, etc.), but up through all of high school I chickened out of several opportunities, a couple that were sure things. I guess I just wasn't ready to give myself intimately in that way (although I had no clue what was going on in my head).
Well, fast forward to a week after high school and it finally happened with a girl I could connect to. I'm not sure why. It's not like she had a great personality, but I think it was that I gathered that she really liked me and that was enough.
Yada, yada, I've had a couple casual encounters (most when I was between the ages of 18 and 20), but nothing compared to my friends who were all over the place. I just couldn't be like that. To me there had to be that chemistry. Plus, being an introvert, I'm shy (in many social situations). I've had ten encounters in my life, and of those ten only half were somewhat meaningful (the others being awkward from lack of connection), and of those five only two (including my wife) were what I would call a true connection of mind and body). Oddly enough, the one other person I felt a real mind/body connection with was someone I met the day before when I was 20. Met her at the beach, asked her out, and the next day we really connected. Had we not lived a thousand miles apart (she was on vacation) we would have dated seriously. We were only together three days but it was the real deal. That came out of a casual encounter, but it wasn't casual sex by any means.
So, it's not just a female thing, really. Sure, guys look at sex differently in general, but I think personality types are far more important than gender in this situation.
If your friend wants to just fool around, it's perfectly reasonable to expect that he might not take it seriously and you might fall in love. It's a risky thing.
But if you don't each feel a true mind-body connection, then it might not be a great idea to get together.
That's just my opinion.