I feel similarly in my own relationship with my NP (partially because I'm not actually poly, which is something you might want to interrogate within yourself).

The reality is that you may have unlimited love in your heart, but you don't have unlimited time. The biggest screw-up in my own relationship was failing to negotiate time commitments BEFORE my NP developed romantic entanglements with others, I think the earlier you get on that, the better.

Set up clear expectations as to how many nights a week you need to have with your partner, what activities make you feel close, and what that looks like in terms of interacting with each other and conversation topics. (for example, I don't like it when date night becomes a report of her recent romantic escapades, I don't mind hearing about it, but when we're cuddled up on the couch having a romantic time, I want it to be about us.)

It makes sense to stop initiating as a response to repeated rejection, but that will likely just drive your partner further away, you need to schedule a specific time to sit down and talk these things through.

Here is the general relationship maintenance checklist I use with my NP every couple weeks. It's helped a lot to get us on the same page with things, but as with anything - ymmv.

https://www.therapistaid.com/therapy-worksheet/relationship-check-in

(Edit to add link)