Well I will agree with you that it is unhealthy for your relationship. Any time a guy is still that attached to his mother it puts a block in the way of having a healthy relationship of his own. I'm actually going to take a bit form the Bible here, it is extremely right in the analogy of a man and woman becoming one and leaving their parents. Until he is ready to let go of this childlike tie with his mother I think it will be a huge roadblock in the way.

However, I think Alexi is right in saying you cant just bring it out like that. In this kind of situation he will be extremely defensive of his mother, and I believe he cares about her more than you, so you would be the one to go first. It is up to you how you handle it in the end, but this is a problem that I do not think can be fixed by anyone but himself, or possibly a therapist .