I (27F) started talking to Aspen (36M) about 6 weeks ago, after meeting online. He has a longterm partner who he is highly enmeshed with (they live together and she is involved to some degree as a coparent to his child with an ex), and they each have other partners (his are mostly casual, she has a long-ish term partner, and they occasionally engage in small group play together). I'm relatively new to polyamory, have been casually dating for several months, and was open about the fact that I am looking to establish a partnership that can provide both emotional and physical intimacy without the relationship escalator pressure. In the month before I had to leave town for an extended work trip, we went on several dates, and established that we have great physical chemistry and get along really well. Since I've been out of town, we've kept in daily contact via texts and phone/video calls, all of which really strengthened the emotional intimacy in our relationship.

3 days ago, he messaged me and let me know that due to problems with his NP, they are closing their relationship for an indefinite period of time and that he is unable to provide me with any details as to why. He essentially (although not explicitly) asked for immediate no contact, and said that he would reach out to me if/when the situation changes. In the moment, I agreed to everything he said and said that I would respect his wishes, was hoping for the best, etc. As I've had more time to process, I'm really, really struggling to deal with the emotional whiplash of going from what felt like the start of a really beautiful emotional connection ( a healthy dose of NRE, obviously) to feeling completely blindsided and disposable. The past few days have been a constant cycle of grief, tears, and spiraling over all the possible reasons this happened/what I could have done wrong. I know that relationships end for any number of reasons and that he by no means owes me anything, but I'm having a really hard time accepting my complete lack of agency in this choice, as well as the prospect of never being able to have a conversation about it/seek meaningful closure.

I guess what I'm looking for with this post is to try and reach some sort of understanding of whether a. the way he handled this and b. my level of emotional involvement/response are "normal" (for want of a better word). Are there specific things I should have done, or known to ask about/for to protect myself? Or is this outcome just an inherent risk of dating people who are so enmeshed with established partners?

At this point, the idea of getting involved with anyone in a highly enmeshed relationship again seems impossible - I can't imagine trying without becoming ruled by my fear of this exact thing happening again. I would really appreciate any advice you all have to offer on strategies I can use to manage my emotions around this situation to mitigate that possibility in the future. I'll also take any and all encouragement to continue maintaining no contact - breaking a boundary like that is so antithetical to the way I conduct myself in/around relationships, but I'm really struggling with the urge to reach out and demand answers, or at least accountability for the fact that I am dealing with the emotional consequences of his choice alone.