I've been thinking some more on this, and about the impact that returning to study has on personal relationships.
It's hard. Any big change can be hard, and returning to study (whether as well as or instead of work) seems to me to always be both a massive practical change and a massive headspace change. I haven't got a bad word to say about how my partner has responded - she has been fantastically supportive and understanding - but I still often feel really frustrated by being so much less available than I used to be. Once in a while I feel a sort of distance - I've got a whole new sphere of me, and with all the interest and support she's expressed she's still definitely not within that sphere, and (again, emphatically, this is very much once in a while) it does feel like there is a massive distance between where my head is sometimes at and where hers is / where mine used to be. That's in spite of not really ever having been a 'merger' couple - different social lives, different jobs etc ; I think the difference this time is that the new stuff is very all-consuming, and exciting, and I sometimes feel a bit guilty for being so immersed in it.
That may not make any sense at all.
It's not just my relationship with my partner - it's been relationships with friends too, being unable to get people to understand just how tired I am / how little time I actually have available, though this perhaps is very specific to combining uni and work.
I don't know how any of this applies to people who don't have a partner - of my uni friends, all bar one is in a serious relationship (I don't know whether this is representative of mature students / students on my course / whatever, or a random coincidence, or whether it's just one of the things we have in common as a small subgroup ..) so I don't really have much alternative experience to draw on. I wouldn't trade in my situation for the 'convenience' of being able to be completely selfish in the way I imagine many 18-year-olds are able to, but I think it probably makes for a massive massive difference. I think that might be the chasm of understanding between me and long-term friends who went to uni at 18, actually - I wonder if they can't understand how it's different to have established a non-studying life and then fit uni into that (even if I had been able to give up work and 'just' study instead of that), compared to simply leaving home and moulding a student life, fitting a job into that.
I went to an orientation day thingy before I started uni, and there was a talk on what to expect from returning to study. Those are the two things I remember - time ("you need to understand exactly how many hours a week you'll need to spend studying, and then you need to sit there and work out how you're going to fit them in ; you'll have to give something else up, and you need to decide what it will be") and relationships ("whatever your set-up now, it's going to come under a lot of pressure from change ; you need to appreciate it's going to be a difficult surprise for the people around you, and some of you will definitely come under pressure to abandon your course and go back to how things were before .."). I can't remember anything more, but maybe that's just stuff I've forgotten because it hasn't become any part of my experience.