On Saturday eve DP and I had a big but petty argument. It's not often we do that but it does happen occasionally, he'd just had a long day at work and I'm really stressed out finishing my masters, I feel like I've been permanently in a bit of a low mood recently. The 'argument' was both our faults. And fwiw I've been a bit low recently too as we're moving in together soon and spending 90% of our time at his place, most of that time he plays video games- I wanted Saturday afternoon off work to spend with him, we got back to his house and he immediately started gaming, as always. I suppose I was annoyed about that too which probably influenced my bad mood.
I had a lot of MA work to do (that was due today, it's finally over!) so I decided to go home, I still felt angry and didn't want to argue anymore, I felt like I needed a calm quiet place to work away from it all. He asked me not to go and said he was cooking me something for dinner, but I said it was probably better if I did because I needed to focus on my work and I didn't want to sit in another room knowing he was annoyed with me over something so silly. He said then that if I apologised we'd be fine, but I said I didn't want to apologise because it wasn't solely my fault at all - and DP seems obsessed with having me apologise, or accept blame for arguments/disagreements and I HATE it. So I left.
Yesterday morning I woke up feeling a bit mean about the whole thing so I texted to say I was sorry, I was angry and just needed a bit of space to do my work but I was genuinely sorry for what'd happened. He read the message and didn't respond. Ditto the next five messages I sent (they weren't long, just a line or two saying sorry/please talk to me/what's going on). I sent a message saying please just respond and tell me if you want more space, I'm just starting to worry. No response!
I was meant to be going over to his that evening anyway, so I still went at about 8pm and he wasn't there, his flatmate said he hadn't been there all day. It got to about 10pm and I started to get seriously quite worried/upset. It's not like him to maintain silence. I texted the few friends I thought he may be with, and all of them said they weren't with him. He did finally text back saying he was fine and would talk to me later.
He finally resurfaced this morning to say he was just really angry after what happened on Saturday and wanted a day to himself. I totally get that, of course, but it felt cruel to not just say that yesterday when I was going out of my mind with worry (and trying to finish a huge essay...).
I also am worried still because have no idea where he was all day. But I'm going to ask him tonight when I see him. I know on MN everyone is quick to say he's cheating but honestly I really really don't think that he was. I just am slightly baffled. I can say with faith I know he hasn't been seeing someone else already, so if it were that he'd been with another woman all day, it'd have had to all been arranged and happened in one day which seems just a bit 
but that said, most of our friends are mutual and I can't think who he would've been with all day if none of them. That and the fact that he wouldn't answer the phone all day, and I know he's skint right now so I don't think he'd have gone out drinking all day too. Not sure if he knows i went round to his house or spoke to friends so at least if something awful has happened and he tries to cover it up, I'll know he's lying.
Was I overreacting to be upset about him ignoring me all day? Was me leaving on Saturday a really horrible thing to do? :( I suppose if he'd have done that to me I'd be raging.
I feel like maybe I was, because we are quite a 'close' couple and stay in contact a lot, see each other every day kind of thing.