Concern

First of all, I do sympathize with you. Getting rejected really sucks. It's virtually impossible not to feel slighted somehow. It is not my intent to further hurt your feelings, but based on what you wrote, I would say that you are the one handling the situation poorly. And that says a lot, because when hearing one side of a story where someone is complaining, it is usually much easier to side with the person that is telling you their side of the story. Here are some important things to consider, not necessarily in order of importance, but hopefully will be helpful to you when you're ready to hear them.

1. As adults, we are not entitled to others' feelings and time. No one should force you to be their friend or lover and you shouldn't try to force that on anyone either. Your time and attention in a relationship needs to be freely given. In my opinion, a relationship is not worth it if someone wants to leave it and the other person is continuously compelling them to stay.

2. I think I saw the term ghosted somewhere and that he blocked you for "nothing", I think neither of these are the case. Ghosting means to disappear without an explanation. And a reason was given that is not "nothing". People get blocked on here for nothing all the time, and I've even spoken out against that in some cases. That is not what happened here though.

3. Not feeling a spark/vibe IS a good reason not to pursue a romantic relationship or friendship. Also, given your position, there is virtually no excuse he could have given that would be "valid" to you.

4. As @SnowMinx said, it was his choice to make and there is really no point in speculating what the real reason(s) were. You're only doing a disservice to yourself here.

5. You spoke about feeling undervalued, and I get it...but consider that by clinging to these thoughts you're having is under-valuing yourself. When something is valuable, and someone refuses it, the attitude tends to be "ok, buddy, your loss! Someone else will come along and maybe even pay more for this than you were considering in the first place!" Being hung up on their refusal communicates the opposite of value. Now, I do believe you have value, but you're not acting consistent with that is the point.

6. Time is one of the most precious things that we have. And everyone has finite time and resources. One cannot expect someone to just collect relationships non-stop. Having a friendship could mean not having time for another kind of friendship or romantic connection that is actually desired. There is nothing wrong with a person's decision to not want a certain kind of relationship in their life.

7. It should also be said, that the nature of your connection did not obligate him in any way to stick around. If you had kids together or something like that, and he bailed, that's a whole other discussion.

8. I understand that you do not agree with cutting ties with someone who is a positive influence to you, and I would agree! I wouldn't want to do that either! BUT...a relationship is not JUST about you...one side of a relationship feeling they have enough positive benefit to make the relationship worth keeping is not enough. This needs to happen on all sides.

There is also another thing I wanted to touch on that hasn’t yet been discussed. You said here:

“He has a 24/7 dynamic with his nesting partner in a V with her husband. I told him that I was concerned that that nesting partner was all consuming and bringing in another relationship might be hard.”

This part concerned me a little, and I’m wondering if perhaps this may have been a factor.
Not saying this was the case here, however, sometimes what can occur when a new person is coming into the mix of an already established dynamic is that there is a secret hope that they could potentially become “the favourite” or even worse, a hope that he may leave his partner for them. This may have been something they’ve experienced in the past, so it could possibly create a bit of a knee jerk reaction. The connection between his already established partner and himself (as harsh as this sounds) kind of isn’t really your business. The reshuffling and reestablishment of how things will work involves you of course, and your concerns about how much time and quality connection you have together is most definitely something to discuss… but perhaps not in that way. Showing signs (especially early on) of vying for or “fighting” for attention in a poly situation does kind of raise some thoughts of whether that “competitiveness” may be an ongoing issue down the track.