I definitely agree with what Maggie has to say - it's really something that you can't force and that you leave up to him. I'm sure it's hard right now with him being so clingy, but just take him around other people and make sure that he feels very, very safe....and if that involves having his head burrowed into you at all times, so be it. Also, just what Maggie said, make sure that the people you do bring him around are people who will keep their distance and let him get to know them on his terms.