Hi op, just wanted to say I've been where you are in a way. I was 34 years old, living with my ex abroad when we split up, and I couldn't move home for several months afterwards, until I finished my degree. Our relationship basically died in the autumn, and I moved home the following May. We lived in a two bed flat that whole time, I slept in the spare room for most of it.
It was tough, it felt like I was in a constant negotiation of our relationship terms. Every conversation we had was just full of complex, excruciatingly painful subtext and half said things. We had some ferocious rows, and some weird moments where things seemed almost normal, happy even. which was a head fuck all around.
I knew it was ending, he probably knew too if he really listened to what i was saying, but he wasn't accepting it. He made promises of different behaviour, which rarely came true, and even if they had, it wouldn't have washed away the previous ten years of his behaviour to me. When he did manage to behave like a decent person, he held it over me, as if to say 'see how much i'm doing for you, changing my behaviour for you, and you're just ungrateful for not falling right back into line.' That his pathetic efforts didn't work to reel me back in really pissed him off. On the other hand, literally in the airport, as I was getting on the plane to come home finally, he was still talking about our future.
It was, in hindsight, a nightmare situation, and once I did get out of it, I needed a long time to recover from it.
But I did get out. Getting on that plane was a relief in the end, because i just didnt have to deal with him and his emotional vacuuming any more. I still had times afterwards where I questioned whether I made the right choice, and I definitely took a long time to get over it, both the relationship and the period of breaking up as well. But it was without a doubt the right decision for me, and I would never in a million years go back.
You will get through this part of your life, and hopefully you will emerge stronger and more in tune with what is right for you. I know I came out of it determined never to be in that position again. So far so good on that!
Keep breathing, one step at a time, and focus on your job and your start date. You will get there.