I'd say don't try to. It's not worth the effort and the stress. Life is too short to be spent worrying about the whereabouts of your girl/guy.  If you feel she is not spending enough time with you, or not honestly sharing her whereabouts when you ask her, there isn't much you can really do. If you can't trust her to do the right things when she is not with you, then maybe you  need to think whether she is the one you want to be with. Maybe there is another girl for you some where out there,  someone  you can trust and not have doubts about.

Before the bra-burning feminists on Sajha go bombastic on me, let me say that I would give the same advice if it was a girl in Jiban's place asking that question.  Not worth the stress  - boy or girl.

But that's just one person's thought.

Good luck