Ah yes, it'll be bloody Fortnite. It's kiddie crack.
I have a 14 year old who is virtually addicted. We are fairly strict in that we will take no nonsense whatsoever, so if he is rude to us etc then he basically has to come off it for a few days. We will never allow a PC or console in his room. He will have to be living in his own place before we'll allow that.
His dad and I both work FT, key workers, but we allowed him and his older brother to stay home rather than go to school during lockdown (he could have had a keyworker place). I trusted him to be getting on with his work online at home and then I discovered weeks later that he'd just been going on fortnite during the day and got WAY behind in his work.
I went ballistic, he cried, said he'd do better etc etc. I really thought he'd learned his lesson. So we gave him a second chance. And guess what, he did the EXACT same thing again a few weeks later. I had to contact school and apologise and make a plan with them for him to catch up etc. More tears from the boy........
He went back to school in Sept and I was still making discoveries. He had a twitter account I hadn't known about, in which he'd slagged us off royally during lockdown and asked if anyone would like to swap parents. 
He really doesn't know how good he has it, and actually, someone said to him on the thread "Actually, I only have one and he's not very nice, so I'd swap with you any day". Doubt it went in though.
What's embarrassing is that I work in a boys' secondary school and know EXACTLY what they're like (hence why I will NEVER agree to a TV or console, or any device in their bedrooms while they are living with us). I see the consequences of their screen addiction with my own eyes. I thought my son was different. Ha! Naive or what?
We'd had all the talks, and warnings including from Dad, who can raise his deep voice just a little bit and both sons know we mean business. We are not soft. We are assertive, and the kids listen and don't argue back. We don't even have to shout. They are well behaved in all respects. But this one bloody thing, the Fortnite addiction with DS2.....it's an absolute nightmare and has changed his behaviour so much. Shouting, slamming the keyboard in anger etc etc.
Honestly, it will be the gaming. Boys and hormones from around age 10 up, plus Fortnite equals an explosion waiting to happen. It's terribly tempting to let them go on it for a while as you know it will give you some peace for an hour or two so you can get on with your uni work etc. But boys that age and into teens desperately need to be kept off the screens and have some boundaries, and lots of contact, chat, activities with good adult role models.
They will say they hate you for restricting their use, and all that, and slag you off to their mates etc. But that's what pre-teens and teens do. Please don't take it personally. Ignore all that. Shrug it off. YOU'RE in the right, and you're doing the best by them. Be strong, have the boundaries there, and it will do him AND you a favour in the long run.
Is there any other activity he enjoys doing WITH you? My 14 year old enjoys watching certain telly programmes with me. He enjoys some box games, and it's really good bonding time. We talk. He also likes some of the same music I do, so we enjoy listening to that together.
Above all, please try and not let his outbursts affect how you feel about him. When you work in a boys secondary school, you come to realise that most of the badly behaved boys are not all bad. There's usually a reason for their outbursts, even if that reason is just that they can't cope with their hormones, and the way it makes them feel all over the place. These are children, we have to remain as calm non-emotional adults, and just try to guide them through the awfulness of the pre-teen and teenage years.
Please take this as just a matter of fact, it's not a criticism or blaming anyone, but the split could well have had an impact, and his anger at the situation may just be playing out in his behaviour. Outbursts. Telling you he hates you. Ignore it all. You need a tough skin. This is not him speaking, it's the hormonal, upset, game-addicted side of him speaking. He WILL love you underneath all that, he really will.