The warmest of welcomes to you at such an incredibly challenging time in your life.
It's interesting that you mention how it feels like you're going deeper into a black hole. Through my own experience with depression in the past, I liken it to a depression or a well of sorts. Based on a whole variety of factors, at times in life we can feel ourself 1)flying high, 2)being grounded or 3)being below grounded/below ground in a depression. There can be so many different levels to that well, from the entrance right down through to rock bottom and then there's every level in between. If we're a feeling sort of person, we can often feel where we're at in that well.
I've found that sometimes it definitely pays to wonder 'What/who raises me and what/who brings me down?'. While some of it's not always obvious, some is. While you've been wondering what exactly could be at play, you've touched on a number of possibilities. Btw, not sure if it's relatable but I've found the deeper I can go into a depression the deeper the wondering or questioning can become, as a side effect. Questions like 'Why do I suffer? Why am I here? What's the point? Why can't things be easier?' and on it goes. While there can be a number of things that can offer us the kind of energy we crave in depression, I've found there's nothing quite like positively mind altering revelations (to the deeper questions) to offer sudden bursts of energy, also known as the kind of inspiration you can feel. Typically, I tend to naturally dig deep even when I'm not depressed and those times are at the end of the year (before the new year) and when my birthday hits. These are typically times of reflection, looking back at what I've achieved or haven't achieved. So, it can either become a time where I pat myself on the back or my inner critic comes to life in the most brutal ways regarding my lack of achievement. For yourself, both of those days happen around the same time of year and I can't help but wonder whether you tend to reflect in the ways I mention.
I believe that having people around can serve us in a couple of different ways. They can lead us to feel some of the things we need to feel and they can act as a welcomed distraction from the inner dialogue that can come to test us. When they're not around as much, the consequences become a lack of feeling what we want or need and a lack of a break from that internal chatter which can feel like a form of torment at times.
