Want to express that I have romantic feelings for my autistic friend but unsure they feel the same

Long story short, I have a friend who is on the spectrum. When we first met, we seemed to have an instant connection. We would hang out and do all nighters all the time. We would flirt and honestly just have a lot of fun together. Nothing sexual ever happened between us. We never went on a date or anything. But then for some reason, they stopped flirting. We seemed to be getting closer and they just… took a million steps back. They now treat me so differently to everyone else. I’m so hurt and so confused. I don’t want to have done something wrong. I don’t think I did. They will still agree to hang out with me sometimes, but they hardly talk. And yet when we say goodbye, they will say “talk to you later” and I’m like… but you barely spoke to me?! I figure if they didn’t want to hang out with me they would just say no, but I don’t understand. I don’t understand why they went a whole 180° on me when we started to get closer. I’m ADHD also btw, so I struggle with a few things myself, which is why I thought I’d come here and seek some advice. I want to tell my friend I have feelings for them, but since they’ve taken so many steps back after giving to many indicators that they were possibly reciprocating the feelings, I just don’t know what to do. Have they pulled back out of shyness? Overwhelm? Or are they just not interested after all? I know I can be full on when I’m interested in someone because I want them to know they are amazing in my eyes. But it seems like me saying nice things to them also pushed them away. I’m so confused and just really don’t want to do the wrong thing here. I care about them a lot and just want them to feel safe.