<human>: Can you provide a brief rundown of the text in within 3 sentences?

Not much to say really.  We've only been seeing each other for just over a month, and it's mutual that we really like each other.  However, she told me last weekend that she's been in an open relationship with another guy for a long time.

Obviously I don't consider this a giant issue right now, as when people first start dating they're in all sorts of potential relationships.  However, I'm a bit concerned as she expressed that she has complicated feelings for him and she's never been in a position where she had to make up her mind between him and someone else.

We've barely been seeing each other long, so I don't want to risk pushing her away by making demands.  But at the same time, if we continue seeing each other this just won't work for me.  How do I broach the subject without forcing her to eliminate someone who she considers a great friend from her life?  How do I make this work without making it an ultimatum of "it's me or him?"
<bot>: Been dating for a little while, she's was honest about an open relationship with another guy and has complicated feelings for him, not sure how to push for exclusivity without it coming across as an ultimatum or pushy.