In my opinion you did the right thing. Nothing wrong was done. It is very smart for someone who smokes to smoke away from the children. Yes, they can smell it on you, and it's bad for your own health, but you are smoking away from your child so that is the right thing to do in this situation!! Many people need to realize that smoking is an addiction and is not easy for all people to quit. I smoked for a year and quit one day just because, and I had no problem, but others struggle for years. I suggest you try to quit, but know that if you struggle at it, or slip up, it is okay, you'll get their eventually. You very obviously love your daughter, and she knows it, and that is all that matters!
And on the note of marriage. Everyone must do what is right for them. It is not anyone's business how you live your life! My partner (sounds better than boyfriend) and I have been together six years. I have no desire to ever marry, but I do want to be with him the rest of my life. He doesn't want to marry either, but he has told me he would if I changed my mind. He is 33, and I am 26. He has two daughters from a previous relationship. So when we are out with them I always get comments and glaring looks because I am young and they assume the girls are mine. (the girls are 10 and 12). Although it is annoying, I could care less what they think. There are plenty of super young mothers out there that are the best parents. Married, older couples are not perfect either. It has nothing to do with age or marital status!! I has to do with your maturity, and your heart!!
I wish you all the best!!!