How do I keep my 18 month old son in his room throughout the night?

Hi, Im now going on 4 months on my second child and I know that when my new arrival comes it's going to be too difficult to try and feed and be there with my 2 year old. My son is soooo attached to me right now, he doesn't even like my husband to hug me, and at night my husband cant put him back to sleep, it has to be me. Now with my son, he doesn't have a special blanket, he never took a pacifier or anything of that sort, but the one thing he is attached to, especially at night is my hair, I really do think that it is his security blanket or something. How can I brake him of all this before my new baby comes? Please help