Melissa,
To start with I feel that it is completely inappriopiate for any girl (friend or not) to be calling your boyfriend and telling him that she loves him period!! It is unacceptable and your boyfriend should be telling her the same thing. The fact that he allows this to continue shows a complete lack of respect for you. Would you do that to him?
I do not think that this is about you wanting him to stop seeing his friends? Is it? From what I have gathered you just seem upset that boundaries things are being crossed (which they are) and you seem to want more from this relationship.
IMHO it does not matter if he has known his friends longer then you. You are the one who is in a relationship with him now and he should start acting like it.

Jessica