“Sucking at something is the first step towards being sorta good at something.” - Jake The Dog

i pride myself on

This. This right here is what’s fucking you up.

You’re hanging your sense of self worth on whether you played amazingly in a practice session, and playing amazingly all the time is not the point of practice. Like, at all. The point of practice is to make mistakes, to analyze and fix those mistakes, and then to reinforce your victories through repetition. If your practice sessions are just you sounding good playing the things you’re already good at playing, then you’re not really practicing. So if you find you’re not playing well that day then just slow down, look at where your mistakes are happening, look at the mechanics of how your hands are moving, play as slow as you need to in order to fix what’s wrong. Repeat that until the mistakes stop happening. That’s practicing. That’s what practice is for.

I’ve been playing for over 30 years, so maybe I’ve become a little more philosophical about this stuff with age, but I don’t even see the point in thinking about practice in terms of whether a session was “good” or “bad.” You have to take a much longer view of what you’re doing. Each practice session, whether or not it feels productive, or feeds your ego or whatever, is a step toward a goal. Each goal is a mile marker on a long, looooong journey, which doesn’t have any real destination or end point. If you’re interested in progressing as a musician, you have to keep pushing yourself to attempt things that are beyond your current ability. When you do that, a lot (maybe even most) of your practice sessions are going to be messy, frustrating, and maybe even a little bit tedious. You just have to get comfortable with that. You don’t get better without that. You just have to sit down and do the work, and trust that if you follow the process it’ll eventually get you where you want to go. You just have to keep putting one foot in front of the other.

when i try to play something, and the tuning is weird, or this pedal got nudged and sounds bad, or i try a new song and fuck it up

Just FYI, the first two things in this list are immediately fixable in the moment. If you’re letting them affect your mental health, that’s 100% on you. Tune your guitar. Set your amp/pedal EQ to where it sounds good. Someday you might be successful enough to hire sound engineers and guitar techs to do it for you, but until then it’s all you.

The third thing is just part of the process of learning a new song. It happens to everybody all the time. Nobody is exempt. There is zero point beating yourself up about it.

Finish by playing something that you like and can play well, and remember that you’re going to have bad days, but you still enjoy it :)

Some days are just gonna suck, just like some days are going to be really good. Just roll with it.

I like this blog post that highlights the difference between “practicing” and “playing” the guitar. Highlighting what others have said, practicing the guitar should pretty much always be difficult. But it sounds like you are upset that your guitar “playing” is occasionally difficult. And - yeah that never really goes away. The good news is that you can practice your way out of it from an outsider’s perspective. You will never stop having bad playing days, but you can practice to the point that your bad days sound better than your current good days.
My buddy and I started playing together in high school. Natural talent only took us so far, so we competed to get better than one another. (Some other friends were in on this too, and we all became better musicians for it.) Anyway, I started performing less and less as my college obligations took over while my friend continued to practice every day. My friend is now a professional musician who has been on multiple world tours. We both still have bad days, but his bad days now always sound better than my best days, just because he stuck to it harder and kept pushing himself to get better.
In short, the precise practice of particular problematic parts of performing predictably improves playing prowess. I.e., “practice makes perfect.”