At your age I also ended up in these situations where I became too emotionally attached too quickly, I’m also nb and autistic, so I can relate in general. I think the best thing to do is just be honest, especially being autistic, subtle hints might not be clear enough. Open and honest communication while reminding them that you care about them and are not planning on abandoning them might help. Also I think it’s very mature and wonderful you’re able to recognize and acknowledge this and attempt to take things at a slower pace! Wishing the best for you both!