An important thing about poly dating is that sometimes people get distracted by the poly part of it and miss the fact that the relationship is just not working. Maybe you and she just don't click.
If you were dating a monogamous woman for a few months and felt she'd been distant from you the whole time, ever since you'd first met, what would you do? You would probably break up with her, or maybe have a talk where you state your feelings, ask why things seem so distant between you two, and then maybe decide to break up, based on her answers.
The fact that she is poly and has another partner is not the problem or the reason for her being distant. I'm sure it feels like that's the issue-- that things are going well with her and her other partner, while things aren't taking off with you. You are comparing yourself to the other partner, wondering what you're doing wrong, why your relationship with her can't be like her other relationship.
But that's the wrong way to think about it. When people date, sometimes they just don't click the same way. Sometimes their feelings don't match. Sometimes their communication styles and interests don't mesh. Sometimes they just don't vibe with each other.
Poly can be hard, because when that happens, you may also see how things are going better in your partner's other relationships. Of course that's very painful! But take poly out of it, and you have a woman you've been dating for a couple months who's been distant the whole time. Sounds like the relationship isn't taking off, for whatever reason. It's not BECAUSE of her other partner. It just is.
I'm sorry.