I'm sorry to hear you're in such a dark place at the moment. I can understand you being upset about finding yourself here again. Anorexia has a way of sneaking up on people and by the time its noticeable it has tightened its grip.
I can see why the prospect of gaining weight is scary, but the more you lose, the harder it will be to recover. Perhaps start out by making sure you don't lose any extra weight and focus on maintaining where you are. If you struggle to remember to eat, maybe set reminders on your phone. Aim for small snacks or means throughout the day to keep your energy levels up. Hopefully you will also get emotional and cognitive benefits from that, like feeling less down, being able to concentrate more and having a less obsessive relationship with food. And lastly, don't berate yourself too much for relapsing. It happens, and now you know to be super careful if you get physically unwell again in future. You have overcome this before, so you can do it again.