I don't have any real advice, other than to try to see a psych if you can (it takes a lot of the burden off if you get medicated and therapy - not all, but a lot) but I wanted to let you know you aren't alone here. I spent my 20s in much the same way - spending... more time than I care to admit getting mediocre grades in college and fighting my mental health every step of the way. Always felt like a failure, like I wasted my potential. Hell, I still feel that.

Spent most of my 20s living with my grandparents and loathing myself. Didn't get out until the tail-end of my 20s, and even that was half-luck. Getting out... helped. I still struggled with depression and suicide, but a lot of self-recrimination ended once I had some manner of independence. And hell, I never held down a steady job through all of my 20s. You aren't alone. It's not some exceptional failing of you or your character. And it's not hopeless. I hope (ha) that doesn't sound too patronizing. It's hard to tack between acknowledging the seriousness of your issue and your struggle while trying to emphasize that triumph is still possible.

Guess all I can really say is, as a survivor of multiple suicide attempts, suicide is... not as appealing as it might first seem in the heat of the moment.