Fortnite is damaging all my relationships and it's literally making me have a mental breakdown
Are you sure it is Fortnite that is giving you these feelings?
Yes. It's all I do and think about. I can't concentrate on anything else.
Are you going to stop playing Fortnite? It is bad to keep doing activities that make you damage your relationships.
But I don't want to stop.
If you don't want to stop playing Fortnite even though it's hurting you and your relationships, then I think you have a serious problem. You should talk to a professional about this, because continuing to do something that's bad for you isn't going to work out well.