I admire this girl for getting out of a bad relationship with someone who had a drug problem. Probably him getting clean was a last step to see if the relationship would ever work out.
Now that he is clean, he's only been clean a few months, and that is not long enough. But she may very well feel an obligation to re-kindle that relationship, now that he is the man she wanted him to be- clean and sober.
While she is teetering on that slippery slope, and says that she is feeling confused between you and her ex, and doesn't know what to do, you tell her she needs to make her own choice.
To me, that says that you are interested in a relationship with her. If she chooses you, and then you say you don't want a serious relationship, where does that leave her.
While you want to have each date with her, as though it were your last, it sounds like she is on the verge of each date leading to another date, leading to a relationship.
Have you actually told her you aren't interested in a long term relationship? Or that you are not ready to commit to a relationship with her?
I hope you have, because if she chooses you, which you know she is wrestling with right now, and then you speak up, that doesn't seem very honest or fair.