Does weed make you forget things?

I'm asking because my brother just came into my computer room looking for headphones and i took his earlier this week so i gave him them back. He was like "when did you get that"
Thinking he was talking about the headphones i laughed and said i stole them from your ipod on the counter and he was like no that, and pointed to my ipod. I was obviously confused and i was like "...umm i got it for Christmas..." "oh i didn't know that."

I mean it wouldn't be a big deal, were not that close so it wouldn't surprise me that he just never found out but he helped me set up the Wi-Fi on it. I know he knew, and i also know he wasn't high on Christmas.

This is worrying me. If hes high right now, which it didn't seem like he was, i don't know how he would have forgotten. My guess is that hes gotten into a worst drug. I don't know what to do, or if i can help him at all. The last time i tried to help it didn't end well and we got in a HUGE fight. Ending with him telling me if i told anyone about this he would 'punch me in the face.' What else could cause him to just forget something like that. So random. I don't know. If i talk to him again I'm afraid he will just stop talking to me altogether, hes family, i love him and i don't want to lose him. No matter how stupid hes being.