I feel for you, jdalpino,
I'm in a similar situation, and it's taken me a year to think this through.
If you're an affectionate person, and long to allow yourself to be, I don't think it's healthy for you to have to supress it. You shouldn't have to surpress anything about yourself - this is who you are! It's unfortunate that he is not affectionate, and it doesn't make him wrong, but from your testimony it seems that it doesn't feel right to you, either.
The "roomate" explanation may be true, but it sounds a little manipulative, if you ask me. He's got the upper hand in this situation, does he not?
I think you've got to approach him, directly and truthfully, about how this affects you. Let him know that, despite his reasons, this is hurting you. If he is unwilling to compromise, as you have already been doing, then I think you should seriously consider moving on. How successful can this kind of relationship be in the future? There may be nobody at fault here, but that doesn't change the fact that your needs are incompatible with his.