I can relate so much to this, and I dealt with the same issue for years. After studying music in college, I felt burned out and thought I was done with music. Years later, what I've finally realized is that I was so worried about being successful that I didn't let myself make the kind of music that I love, and I stopped enjoying it. I realized that not only did I have unrealistically high expectations of myself, I projected those expectations onto everyone around me, especially my mentors. I spent so much time studying composition but so little time actually composing, and that was the most stressful part. I'd say the stress comes from thinking about it, and the only release is doing it.
But the thing is, music isn't about being the best. It's about getting people to feel something. People aren't expecting masterworks from you (yet!), but you might feel like they are. Until you're through this anxiety, just enjoy making it. Know that until you choose to share your work, it can go through as many wild/shitty/insane/vulgar/dumb stages as you need it to. It's safe in your hands until you choose to show it to people. All the unfinished stuff, don't think of it as failure, because that's just a recipe for creative anxiety. There's always going to be a huge pile of discarded ideas relative to finished works. That's just part of the process.
I think often about kids making sand castles at the beach. They get so fascinated by the process and the desire to see it finished that they don't even feel the time pass. They don't say, "I'm going to make the best sand castle in the world! People are going to line up and give me money to see this! I'll be known the world over!" They usually don't even start with a plan. They're just having fun doing it, really getting into all the little details for no other reason than their own satisfaction.
That said, I also agree with Garpocalypse. Competitive drive is often a good motivator. I just released my first indie game online, and even though it's completely free, the first comments were all negative. After the initial sting, I found I wasn't angry. I was actually really motivated to get it right next time. I think that forcing yourself to release your best work and subjecting it to criticism can help you gain perspective. You feel so close to this thing you've made, but as soon as it's out in public, you can suddenly see it objectively, as if you were looking at someone else's creation. And you can learn so much from people's reactions about where to go next. It pushes you to reach new levels.
It's easy to silo yourself off and then get into a really stressful negative feedback loop. I still haven't found my best work process, but I feel like I'm getting there. Right now, it's "Feel safe working on things in private, and then once in a while, release your top choices and see if they survive on their own out in the wild."
I hope you find what works for you. It's a lifelong journey, and your creating music or any other art can only have a net positive effect. You've got this, dude.