Hello all, coming to you all in hopes of a little advice as to how to proceed.

Little background first: My partner (nb30) and I (m25) have been together for almost a year. I’ve been practicing poly for a few years now, and they’ve been doing so for around nine. We both got into our relationship with each other being our only current partners at the time, but with the understanding that it was a poly dynamic. Things have been great overall!
Over the past year however, a number of rather traumatic things have happened to them which we’ve worked through together. A lot of it has directly affected their attachment styles and overall has left them feeling displaced within themselves and their relationship to others. A couple of these things have happened rather recently and is, as such, something we’re still currently getting through (none of it being about us as a couple).

A few months ago, I reconnected with an ex (26f), and a week ago, I discussed my desires to re-establish a relationship with her with my current partner. After setting some expectations and boundaries for each other about this, we came to an agreement that when I caught up with 26f that I would give my partner an update on how it went.
The day came and went, and 26f and I agreed to start dating again and spent the day together. At the end of the evening, I called my partner and updated them on how it went and let them know about 26f and I. They didn't take it great as I had updated them late in the evening and had left them feeling unsure and anxiety built up due to the lack of news.

We caught up in person and had a conversation earlier today in which we discussed the situation at hand and where it came from. I apologised for the lack of a timely response and explained my reasoning but acknowledged that it was a slip-up on my end for not taking a timely response into account.
Eventually, the conversation steered to poly overall, and after acknowledging that there was a lot of build-up of trauma that has left them feeling scarce, that perhaps poly wasn't right for them at the moment, and would prefer the security of a closed relationship for the time being until their foundations of security were rebuilt.
They asked what I would like to do, and said that they understood if that was a deal-breaker for me, and wouldn't hold any hard feelings for me if that was the case.

Now comes the current issue:
I love my partner. I've been with them through a lot of things; positive things in our relationship, and helped each other through difficult times. I don't want to feel like I'm abandoning them in an extremely difficult time, but I also don't want to hold myself back in fear of resentment building between us.
I've been considering my options as follows: break up with them as our views don't currently align on poly, or continue dating them and close our relationship for the foreseeable future (and also end my newly established relationship as it's just begun).
I'm sure I could set stipulations about the latter option such as a promise to reopen again when we can, but I'm not sure.

Thanks for reading all of this, I appreciate your time!
What do I do?