You don't own this game, you're renting it. As such you must use it within certain criteria. One of those criteria is STEAM. Steam is integrated into the game, and you're not going to get it to run without it unless you had access to the source code or some manner of developer tools.

Steam is the copy protection, and I'm sure the user agreement stated that this game must have its copy protection intact.

Go to the steam forums and ask there, they will have a better idea what is wrong.