I speak English natively, but have had a disagreement about the use of "suppose". I say it fairly often to be honest. Things like "yeah I suppose so" or "i suppose we could do that".

But in this specific case they are telling me im using it wrong and that it should be "I'm supposed to".

The conversation went like this: Friend- "You always take things so literal. Blah blah blah" Me- "its not that big of a deal. Anyways, I suppose to explain part of it, I'm autistic and that tends to be a trait of it."

Then they they said it should be "I'm supposed to" and no use of the language supports how I used the word.

So I'm just wondering if that usage is all good and what not. I know for a fact any native speaker would full well understand it exactly as I meant it, and that they are just being sorta standoffish. But I enjoy languages and learning about them so id like to learn from people who understand the language better.