Occupy my mind...
Occupying a person's mind simply means something has taken up the person's mind. That is basically all he thinks of, his thoughts is constantly on that thing or person as the case may be.
Although we know that whatsoever will take up someone's mind to this extent must be really precious to him, hence his dedication to allow it take up his mind.
I would also like to add on a personal note that it is a bad idea to let a person occupy all your mind, because it is like giving someone too much power over you. In this case you might be helpless if the person is not around or if the person chooses to break your trust, it would really be a heartbreaker because all of your mind has been dedicated to him or her. So try to be on a safe side.
I am not discouraging having someone special or allowing them occupy your mind, I am only preaching caution.
Thank you for your time...