Most Helpful Guy
No, I do not think this is true. Many guys are willing to put themselves in that position for sex.
People need to separate sex and love. They are not the same. When you can't separate them, it leaves you vulnerable to being played in this exact manner. They give you the love, and the sex comes along with it. However, if you can separate them, one does not equal the other, they are separate experiences which sometimes compliment eachother, yet they each need their own understanding and unique conversations.
Failure to understand that leads to all sorts of complications. Not that each concept on their own cannot lead to complications, they can, but they are more intimately attached to the concepts themselves, rather than the illusion of both concepts intertwined.
Most Helpful Girl
Somewhat true. I'm assuming a handful of girls out there want a serious relationship with someone and wouldn't think of having sex with someone casual. So in other words they would have sex with a guy who is there boyfriend.
Some guys will be very cunning enough to go through all that just to have sex with the girl (depends who the girl is of course) otherwise going back to the question, there are plenty of girls out there who are interested in the casual fling, making them easier to just get.. Sex.