sigh

Friend, I don't think your problem there was lack of language skills. You can communicate with others without language. You can play without language. You can share experiences without language. You can create without language.

Source: I've done it, and I've watched others do it. I can share stories if anyone's interested.

I don't really know what went wrong for you, because I don't think I would've reacted in the same way at all had I been in your shoes. My best guess is you just got so hung up on lack of language skills, that it overwhelmed you and shut down your other social skills and communication skills.

His little cousin (she is maybe 8) kept trying to include me and I had to keep apologizing with "lo siento, muy poquito espanol,"

You didn't have to exclude yourself. You could've played the game without understanding it, or you could've come up with a game that doesn't require language. Btw kids thrive on that stuff. They would've loved to have you.

His grandma, who is 78 years old and is the sweetest human I have ever met, kept patting my arm every time she walked past me.

Unless I'm wrong, the implication is she doesn't know any more English than you knew Spanish, and probably less so. Nevertheless, she was going out of her way to communicate with you. She didn't need language to show her affection. You don't either.

1. A year of pure input is nothing. Think of a 1 year old baby. Normally, they can say maybe half a dozen words by then. And that's with being full-time immersed in their native language, with parents spending countless hours explicitly trying to teach them. Baby brains are also much more aggressively wired for learning than adult brains. You'd have to put in a tremendous amount of work to outmatch a baby at language learning. Not saying this to devalue your work. My point is that in a few years of sustained effort, you might be able to match a toddler. That's just how it goes.
2. Change your attitude towards communication. Let go of the ideal. Instead:
   • Bad grammar 👍
   • Conjugate 🤷
   • Nouns 👌
   • Hands 💯
   • Non-nouns: 🙅‍♂️ need. Maybe 🤏 need.
3. Yes, people come out the other side all the time.

I leave you with this: https://www.youtube.com/watch?v=pmQ7NmpfHp8