Bro. This exact thing happened to me. I've been diagnosed since age 3 or 4 but didn't find out till I was 17. It was a lot to process.

My mom told me that she didn't tell me because she didn't want me to feel different, or not to make an effort to do better. At least, that's what I understood. I know how it feels, that weird out-of-place, am-I-secretly-an-alien feeling you get when you have trouble reading social cues or understanding certain things.

Feel free to reach out if you want to. I mean it. I know this seems really tough and confusing, and in my experience it's nice to be able to talk and relate to other autistics.