i think she's staging a sex strike. jk

ok, maybe the way she said it wasn't so good but at least she told you that it's what she wants rather than barking "you really need to stop smoking" like an order. it's probably not good she's trying to change you already, but when you don't smoke it is hard dating someone who does. just talk to her and tell her what you said in your post. that it was a lot about how she said it and that it really is your decision and it's an addiction. do apologize for how you acted in the car. that was kinda harsh and she is probably hurt and feels a bit rejected. i'm sure you guys will be fine. she still told you she loves you. it sounds like she may be new at this relationship stuff from what you posted before so do cut her some slack. you may need to tell her that sleeping in her own bed when she's mad or hurt is not good though. it might be a good ground rule to not have either one of you do that when upset if you plan on living together as boyfriend/girlfriend. just talk to her. she loves you.

having said all that why not consider giving up smoking now? yes, it has to be your decision but it does affect her too.