Lesson learned here: sometimes things really aren't as bad as they seem to a poor, nervous, panicking mono in a long distance relationship with a poly with NRE.
FINALLY was able to sit down with Q and talk to him in a calm, relaxed manner without either of us over-reacting emotionally. We were able to bring up the things that the other had been doing that bothered us, and also addressed some misinterpretations that had set things off in the first place- he'd taken my asking for reassurance there at the start to be blaming him for making me feel bad and it made him feel guilty when he was already stressed and exhausted, and I'd taken his reactions as him suddenly turning on me and assumed it was due to him and A suddenly being together. We were wrong on both sides and apologized and were able to reconnect in the phone call. He reassured me that nothing had changed, not how he felt for me or what I meant to him or our relationship, and I thanked him for that and told him how happy and relieved that made me, and he said it made him feel a lot better to hear that. We were able to talk about him and A, and he said that was still on hold, that they were starting from scratch and just getting to know each other and that the most they'd done was chill out and watch TV together. I said I had hoped that maybe we could keep that on hold for just a little bit longer while we all settled into this new situation and he said that was fine. Later when I talked briefly to A to try to reconnect with her, she echoed that sentiment, so we're all good there.
I asked Q about the possibility of starting to try to schedule date nights since his job is going to drastically cut down on our chances to talk/spend time together and he said that yes, he had already been planning on doing that. I asked him if we could try to get a date night in sometime in the next few days and he said he needed to see how thing were shaking out time-wise but that he would check and let me know.
I'm still wishing this week had gone smoother, and can see mistakes on both sides that led to both of us being upset, but I think maybe we're ok now. I hope. I am hoping he will get more settled and that we'll be able to re-establish the closeness we had before...though I'm also telling myself that with the new situation and the new job/schedule, I may have to be ready to adapt to what's to come, things are still in flux, especially with me moving out on my own soon as well. But least things are much better after our talk last night.