Am I just not good enough?

Its possible. People either tell you directly you are not good enough, or they avoid you. We are often treated this way. Its often better to keep to yourself

It is lonely to be autistic, or rather it is more common to be lonely, as only a 2% can be. When I was at Uni I had a terrible time because I was viewed as an odd and unrewarding individual, who was only tolerated when all other avenues were exhausted, I spent a lot of time and energy trying to buy my way into other people good-graces. In a similar way to you, I felt like I was simply a battery or resources to be expended, but never repaid or replenished.
Ultimately I believe that if someone doesn’t tolerate you on your lows, then they don’t deserve you at your best, as such it is better to seek out the resources of the uni and of dedicated-forums and some good will come of it. Autistic people don’t learn through the same means as others, we need something to mimic and we need to create a procedural through exposure, so perhaps it is just a wise thing to do to just follow your interests and befriend those that you find on that road.  
The best time I ever had in education was when doing a level 0 course with the Princes Trust, in which nobody knew me and there was no expectation, there was no reward but the rewards of wanting to attend to next session, those who didn’t want to be there didn’t have to be there and no one knew anyone. If the process of education you are taking-up is not developing your character, not piquing your interest, and sapping your confidence; then that is a toxic experience.

Yes of course others have been and are exactly where you've been in terms of loosing friends and bullying and may I say I am so sorry you've suffered. My son is asd and has suffered the same so I know how it is only too well. Please understand that what I'm going to say to you may sound like a cliché but it really is the truth.My son has been in some really bad ways to the point where he narrowly avoided suicide...We had a conversation and I told him that when he feels down or depressed to that point again don't take that step to suicide and instead just to accept what's going on no matter how painful and just get through everyday the best he can because there will come a day when you will feel better or things will get better etc and that day did come for him and he was indeed happier and said he was glad he waited it out. Try to open up to any close friends or family that you can trust. Also know that you are so much more that you are aware of right now and you no doubt have many things that will bring you joy in the future..there's probably hobbies you could try or learn a language or cook anything but just try.

You probably are good enough. And I'm willing to find out for sure. Please feel free to send me a message; I'd love to have more friends.

Bullying is never acceptable. When it comes to a choice between loneliness and dealing with toxic, I prefer loneliness.

All I can say that many, many people here struggle with this one. Rejection hurts. Autism can get in the way of making friends the way many people would, and it sounds as though you are judging yourself by the standards of neurotypicals. 

Why not look for websites, this one too, and look for ways to network with people here who share the same interests, without trying to look for friends for friendship's sake, which by the way can be a recipe for continued lack of success anyway?

Has anyone ever told you what they mean when they say they find you annoying? It might say more about them than you, but it might be helpful to know. 

Sadly there are plenty of other ways to lose friends. Moving away, cultural differences, when the other wants love not friendship, cancer, suicide,  drinking oneself to death......

So a sharing of mutual interests might help, a compatible spiritual community becaise thos is something that can be as inclusive as family ties with less investment in ego. And would you be in a position to have pets? Companionship doesn't have to be just human.....

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advice from people with similar problems probably isnt going to fix things lol

best thing is though, if they are the type of friend to abandon you they are not your friend anyway and they are not worth your time.... consider it that they filtered themselves out and they are the problem.

i had a friend that filtered himself out... i was bullied alot by everyone and my friend one day said he can no longer be friends or hang out with me because i attract too many bullies and he gets some of the splashback on him from that too... he filtered himself out.... a true friend would be there for you and wouldnt abandon you in hard times. a friend that abandons you is no friend at all, we are both better off without these shallow friends. they are not even up to their own ideals of what they would see themselves as, i bet all these normies see themselves as stern and strong and never leave a man behind and believe in the power of friendship!! but yet in reality they all ditch their mates at the first sigh of trouble all for their own self preservation lol ....the problem isnt you... the problem is them...