"why does he constantly want to know your whereabouts and what you are doing?"
Possible reasons (same for both sexes):
1. An insensitive ignorant who doesn't know how to make people comfortable when conversing with him, asks 99999 questions out of concern/curiosity; doesn't even know other people have a right to privacy. Typically, guys like these are poorly educated. If this is the case and you find him attractive in other ways, tell him in very CLEAR words, he needs to read a couple of good books on the art of communication, EQ, sensitivities...etc. You need to be upfront with this type because they are so thick skinned/headed that any "gentle suggestion" won't "penetrate".
2. A control freak, filled with fear and insecurities, thinking with a mind/psyche that has gone "nuts". Wants to monitor every move of yours; the only goal he has is that he can place you where he wants to, at all times. He needs to "kill you" and turn you into a dead object which he has acquired possession of. This is the ONLY way he can feel safe with any human beings. If this is the case, RUN!
In either case, make sure you ask yourself, "Is this guy the kind of guy I want to be with?" If not, flip the guy into his opposite, and focus on the RIGHT kind of guy, the kind you want to hang around with.