lol, bro, it's one of 2 things:
1.) you've fallen in love.
2.)
OR... perhaps you're just an extremely over-protective, and controlling boyfriend, who can't imagine the thought of his girlfriend acting as an individual, let alone talking to other guys w/out yourself present...

"perhaps" ( seriously note though: in this case I would recommend a psychiatrist) lol
It's not rocket science...! Marry the girl

ha.