I think he's thinking/speaking from the ego. I think a lot of men like to employ the idea that women are possesive of them as a way to boost the ego.
My feeling is that an intimate sexual relationship for a woman is often just the natural progression of a close friendship.
The power of society to condition us to think a certain way is very under-rated. I think it contributes a lot to the problems men have when their partner gets involved w/another man - in light of our current society it's just too emasculating and it becomes hard to reconcile who they thought they were with who they are perceived to be.