What do you think of me getting rid of my girlfriend?
Well, why do you want to get rid of her?
I'm fed up with her smoking everywhere she goes and making my house dirty.
Perhaps you should tell her to smoke outside. It's better to talk through your problems first.
I'm going to tell her to smoke outside and then break up with her. I was looking for an excuse and now I have one.
If you really want to break up with her then that's fine, but have the conversation first of why you're not feeling good in the relationship anymore. Using smoking as an out will just confuse and hurt her, and I doubt that you want to do that to someone you love or even loved.