Should he tell his female friend, he loves her?

My boyfriend and I are having an argument, please help! He has a female friend who is his age, that he has been friends with for 6 years. I believe that "I love you" should be reserved for couples who love each other, however he tells her at the end of phone calls/msn conversations that he loves her. I have no problem with him telling a male friend he loves him, however I think telling another girl whom he talks to regularly and who I've never met is unfair.