Trust is definitely the key. However, your past relationships kind of indicate what is acceptable and what is not. I think its okay to have "friends" of the opposite sex, however in my case I would feel uncomfortable if some chick was calling my BF off the hook 24 - 7 ( unless it was a longtime friend). Just like I would feel guilty about doing the same to him. In my last relationship my bf made me sever all ties with guy friends, i gave into him (WHY who the hell knows). He'd go crazy on me if he saw me even glance at another guy... I think it may depend how jealous/insecure that guy/girl is too.