My husband felt that way too. He was ok with the sex idea-but not the emotional attachment.
But-she can never guarantee you that her heart won't get involved.
There is A LOT written on that topic on this forum. I would start reading if i were you.
Because if you allow for sex-you better be prepared for emotional attachment.
Check out morethantwo.com. I think he has a few articles on that precise topic.
"Love As Thou Wilt"