Marines are people. Of course they have worries. If hes that worried about the girl tho he doesnt seem to trust her much which indicates one or both of them have issues. Either he's paranoid or shes a cheater. Besides, being a free country she should be able to talk to anyone she wishes as long as shes not sleeping with them. If your buddy lets his worry reach the point of obsession and/or it effects his ability to be an effective Marine then he needs to get counseling.