At the end of the day you have to decide. Do you love him enough to stay or is he not the type of person you want to be with any longer..
Secondly, you can't really make him stop. You can try and threaten leaving and things like that but you have to understand that it's apersons choice to smoke, to drink ect.. yes they are addictions but the person has be willing to break that addiction and with will power and determination it can be done but without the want or the need the addiction stays.
Sorry to be a downer on the topic.
I can relate btw. my boyfriend smokes too & I am entirely against it because I know what sort of person he could be without it.