He may be being over protective because he's jealous, and possibly feeling insecure in his relationship with her. However, she needs to nip this in the bud because in the end, over-possessiveness and jealousy will wreck their relationship. Perhaps she could try and develop a few social contacts which they don't share so that she can have her own space and he can get used to dealing with the notion that she also has a life of her own and is not joined to him at the hip. I think she also has to sit down with him and find out why he is so protective or possessiveness and tell him that is having a negative affect on their relationship. Was he dumped badly in the past and is frightened of it happening again. He has to trust her in her friendships with other people of the opposite sex. If he can't, he may well find that one day she's going to cut the golden chord.