Your son must be the clone of mine, because my 13-month-old behaves exactly the same way. Only falls asleep on the boob, and if I'm lucky I can sneak out of bed for about half an hour before he realizes I'm gone and wakes up again. Snuggles right up against me while he sleeps. I'm calling it normal, because there's nothing else "wrong" with him so I don't see why it would be abnormal...