I know how you feel. Loneliness is such a hard feeling to cope with. I also know what it is to be invisible. I've felt that way almost my whole life.
If you are depressed maybe you can see a counselor or a dr. They can help you get therapy or medications that make you feel stronger.
Also choose your friends wisely. Get to know them slowly so you can tell what kind of people they are. If they are unkind to others they might be unkind to you. There are nice people out there. You may have to look for them because they may also feel unlikable. You may be able to help someone else feel welcomed.
Here you will only meet with kindness so keep posting and you will find support.