<human>: Can you provide a brief overview of the text?

Long story short, I've been dating this girl for about a month and a half and we're pretty crazy about each other. I've always had really bad anxiety about anything related to substances; go ahead and do it if you want but it's an immediate deal breaker for me because I'm basically having panic attacks all the time when people are using them near me. My girlfriend hadn't used anything until she smoked pot the other day for the first time (knowing that I have difficulty with it) and when I asked her if she planned on doing it again she didn't really say no. I explained that I can't be with her if this becomes any more than an isolated incident and she's telling me that it feels like I'm threatening to break up with her. I don't want to come across like that but where I'm at currently with this issue I have, I can't be with her if this continues.

Some more pertinent details:
I don't have a traumatic incident to trace this to, I've just always been wired to have tremendous anxiety over this.

This isn't the first time I've had to separate from someone over substance use.

This is the first "real" relationship either of us have ever been in.

Thank you all so much for your advice!
<bot>: My girlfriend might start smoking pot which gives me terrible anxiety and is a dealbreaker for me but I'm worried that I'm being the asshole by ending the relationship if she does.