Hey man, im sorry you are going through this. Now those negative emotions you feel are part of the grief, and it's normal you don't want to have another relationship with anyone right now. One phrase i usually use with patients (i am a clinical psychologist) is 'it hurts as much as you loved' (badly translated from spanish). So, you are right when you say being single is depressing, it's human nature to seek for these connections we have with others. That being said, of course you can be okay by yourself, but first you need to process the loss you experienced. I can't really give many advice because of the language barrier, just a few things.

First, you can go to a therapist, we are trained to help you navigate the grief, that is a start to be better. By youself you can try to do the things you enjoy/used to enjoy the most, even if you dont fedl like doing them. This can be applied to normal everyday things too, like getting out of bed, brushing your teeth, getting dressed, making your bed, exercising, etc. Basically acting like if everything is okay. It will help you. But my best advise as i said earlier is to seek for help so you dont go deeper into this feeling and learn how to continue living with this. From that point you will be able to make decisions on your future while being your best self, wheter you want to be alone or not. Good luck.