Hi A.---You've got some serious decisions to make here soon. I've got to think your boyfriend has some serious issues as you've been together all this time while he is still married. If he 'doesn't live like he is married', why is he, married, that is? Being afraid of losing custody while they are currently living with you seems like a very lame excuse. Hesitating because of costs is another excuse. A good lawyer will take care of all of those details. Sounds like he's content just the way things are.
So what do you want? Do you want to have some stability in your relationship that goes beyond your boyfriend having the same address? Do you want your child to have his last name? I would think it is definitely time to make some decisions and plans for a future together.
At this point I think that you can do whatever you want to do as your boyfriend has no legal rights based on the fact that you are not married. Naming him on the birth certificate has legal ramifications for support, but your best bet is to contact your state's office that handles birth certificates. Can't think of that particular office, but if you search a bit online I'm sure you'll come up with the phone number. Ask them to tell you your options but don't take that as legal advice.
I personally feel you have much bigger issues to deal with than what last name your baby will have. And I hope I'm not sounding negative, this is just what popped into my mind after reading your post. If I were your mom (I have a 27 yr old daughter) I would be insistent in her getting a commitment...at least of divorce...from the baby's daddy. You deserve his commitment. Don't settle for anything less. Good luck...I say my prayers for you. D.